Publications
2024
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(2024) Physical Review C. 110, 6, 064909. Abstract[All authors]
The PHENIX experiment measured the centrality dependence of two-pion Bose-Einstein correlation functions in sNN=200GeV Au+Au collisions at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. The data are well represented by Lévy-stable source distributions. The extracted source parameters are the correlation-strength parameter λ, the Lévy index of stability α, and the Lévy-scale parameter R as a function of transverse mass mT and centrality. The λ(mT) parameter is constant at larger values of mT, but decreases as mT decreases. The Lévy-scale parameter R(mT) decreases with mT and exhibits proportionality to the length scale of the nuclear overlap region. The Lévy exponent α(mT) is independent of mT within uncertainties in each investigated centrality bin, but shows a clear centrality dependence. At all centralities, the Lévy exponent α is significantly different from that of Gaussian (α=2) or Cauchy (α=1) source distributions. Comparisons to the predictions of Monte-Carlo simulations of resonance-decay chains show that, in all but the most peripheral centrality class (50%-60%), the obtained results are inconsistent with the measurements, unless a significant reduction of the in-medium mass of the η meson is included. In each centrality class, the best value of the in-medium η mass is compared to the mass of the η meson, as well as to several theoretical predictions that consider restoration of UA(1) symmetry in hot hadronic matter.
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(2024) Physical Review C. 110, 4, 044901. Abstract[All authors]
High-momentum two-particle correlations are a useful tool for studying jet-quenching effects in the quark-gluon plasma. Angular correlations between neutral-pion triggers and charged hadrons with transverse momenta in the range 412 GeV/ and 0.57 GeV/, respectively, have been measured by the PHENIX experiment in 2014 for Au+Au collisions at √=200 GeV. Suppression is observed in the yield of high-momentum jet fragments opposite the trigger particle, which indicates jet suppression stemming from in-medium partonic energy loss, while enhancement is observed for low-momentum particles. The ratio and differences between the yield in Au+Au collisions and + collisions, and Δ, as a function of the trigger-hadron azimuthal separation, Δ, are measured for the first time at the BNL Relativistic Heavy Ion Collider. These results better quantify how the yield of low- associated hadrons is enhanced at wide angle, which is crucial for studying energy loss as well as medium-response effects.
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(2024) Physical Review C. 109, 5, 054910. Abstract
The PHENIX experiment has performed a systematic study of identified charged-hadron (π±, K±, p, ¯p) production at midrapidity in p + Al, 3He +Au, and Cu + Au collisions at √sNN = 200 GeV and U + U collisionsat √sNN = 193 GeV. Identified charged-hadron invariant transverse-momentum (pT ) and transverse-mass (mT )spectra are presented and interpreted in terms of radially expanding thermalized systems. The particle ratios ofK/π and p/π have been measured in different centrality ranges of large (Cu + Au and U + U) and small (p + Aland 3He +Au) collision systems. The values of K/π ratios measured in all considered collision systems were found to be consistent with those measured in p + p collisions. However, the values of p/π ratios measured in large collision systems reach the values of ≈0.6, which is a factor of ≈2 larger than in p + p collisions. These results can be qualitatively understood in terms of the baryon enhancement expected from hadronization by recombination. Identified charged-hadron nuclear-modification factors (RAB) are also presented. Enhancement of proton RAB values over meson RAB values was observed in central 3He +Au, Cu + Au, and U + U collisions. The proton RAB values measured in the p + Al collision system were found to be consistent with RAB values ofφ, π±, K±, and π0 mesons, which may indicate that the size of the system produced in p + Al collisions is too small for recombination to cause a noticeable increase in proton production.
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(2024) Physical Review C. 109, 4, 044907. Abstract[All authors]
The invariant yield of electrons from open-heavy-flavor decays for 1
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(2024) Physical Review C. 109, 4, 044912. Abstract[All authors]
The measurement of the direct-photon spectrum from Au+Au collisions at sNN=200 GeV is presented by the PHENIX Collaboration using the external-photon-conversion technique for 0%-93% central collisions in a transverse-momentum (pT) range of 0.8-10 GeV/c. An excess of direct photons, above prompt-photon production from hard-scattering processes, is observed for pT
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(2024) Physical Review Letters. 132, 8, 081801. Abstract[All authors]
Searches for new resonances are performed using an unsupervised anomaly-detection technique. Events with at least one electron or muon are selected from 140fb−1 of pp collisions at √s=13TeV recorded by ATLAS at the Large Hadron Collider. The approach involves training an autoencoder on data, and subsequently defining anomalous regions based on the reconstruction loss of the decoder. Studies focus on nine invariant mass spectra that contain pairs of objects consisting of one light jet or b jet and either one lepton (e,μ), photon, or second light jet or b jet in the anomalous regions. No significant deviations from the background hypotheses are observed. Limits on contributions from generic Gaussian signals with various widths of the resonance mass are obtained for nine invariant masses in the anomalous regions.
2023
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(2023) Nuclear Instruments & Methods In Physics Research Section A-Accelerators Spectrometers Detectors And Associated Equipment. 1056, 168563. Abstract[All authors]
The evaluation of the measurement of double-spin asymmetries for charge-separated pions and kaons produced in deep-inelastic scattering from the proton using the ECCE detector design concept is presented, for the combinations of lepton and hadron beam energies of 5 x 41 GeV2 and 18 x 275 GeV2. The study uses unpolarised simulated data that are processed through a full GEANT simulation of the detector. These data are then reweighted at the parton level with DSSV helicity distributions and DSS fragmentation functions, in order to generate the relevant asymmetries, and subsequently analysed. The performed analysis shows that the ECCE detector concept provides the resolution and acceptance, with a broad coverage in kinematic phase space, needed for a robust extraction of asymmetries. This, in turn, allows for a precise extraction of sea-quark helicity distributions.
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(2023) Physical review D. 108, 7, 072016. Abstract
Reported here are transverse single-spin asymmetries (AN) in the production of charged hadrons as a function of transverse momentum (pT) and Feynman-x (xF) in polarized p↑+p, p↑+Al, and p↑+Au collisions at √sNN=200GeV. The measurements have been performed at forward and backward rapidity (1.4
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(2023) Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 1055, 168458. Abstract[All authors]
We performed feasibility studies for various measurements that are related to unpolarized TMD distribution and fragmentation functions for the ECCE detector proposal. The processes studied include semi-inclusive Deep inelastic scattering (SIDIS) where single hadrons (pions and kaons) were detected in addition to the scattered DIS lepton. The single hadron cross sections and multiplicities were extracted as a function of the DIS variables x and Q2, as well as the semi-inclusive variables z, which corresponds to the momentum fraction the detected hadron carries relative to the struck parton and PT, which corresponds to the transverse momentum of the detected hadron relative to the virtual photon. The expected statistical precision of such measurements is extrapolated to accumulated luminosities of 10 fb−1 and potential systematic uncertainties are approximated given the deviations between true and reconstructed yields. The expected uncertainties are then used to obtain the expected impact on the related TMD distribution and fragmentation functions. We find that the ECCE detector proposal fulfills the physics requirements on these channels as detailed in the EIC Yellow Report.
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(2023) Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 1053, 168276. Abstract[All authors]
The recently approved Electron-Ion Collider (EIC) will provide a unique new opportunity for searches of charged lepton flavor violation (CLFV) and other new physics scenarios. In contrast to the e↔μ CLFV transition for which very stringent limits exist, there is still a relatively large discovery space for the e→τ CLFV transition, potentially to be explored by the EIC. With the latest detector design of ECCE (EIC Comprehensive Chromodynamics Experiment) and projected integral luminosity of the EIC, we find the τ-leptons created in the DIS process ep→τX are expected to be identified with high efficiency. A first ECCE simulation study, restricted to the 3-prong τ-decay mode and with limited statistics for the Standard Model backgrounds, estimates that the EIC will be able to improve the current exclusion limit on e→τ CLFV by an order of magnitude. The very high vertex resolution of the ECCE detector configuration plays a critical role in τ identification.
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(2023) Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 1052, 168238. Abstract[All authors]
This article presents a collection of simulation studies using the ECCE detector concept in the context of the EIC's exclusive, diffractive, and tagging physics program, which aims to further explore the rich quarkgluon structure of nucleons and nuclei. To successfully execute the program, ECCE proposed to utilize the detector system close to the beamline to ensure exclusivity and tag ion beam/fragments for a particular reaction of interest. Preliminary studies confirm the proposed technology and design satisfy the requirements. The projected physics impact results are based on the projected detector performance from the simulation at 10 or 100 fb−1 of integrated luminosity. Additionally, insights related to a potential second EIC detector are documented, which could serve as a guidepost for future development.
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(2023) Physical review letters. 130, 25, 251901. Abstract[All authors]
We present measurements of the cross section and double-helicity asymmetry ALL of direct-photon production in p→+p→ collisions at s=510 GeV. The measurements have been performed at midrapidity (|η|
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(2023) Journal of High Energy Physics. 2023, 6, 82. Abstract[All authors]
The electroweak production of Z(νν¯) γ in association with two jets is studied in a regime with a photon of high transverse momentum above 150 GeV using protonproton collisions at a centre-of-mass energy of 13 TeV at the Large Hadron Collider. The analysis uses a data sample with an integrated luminosity of 139 fb−1 collected by the ATLAS detector during the 20152018 LHC data-taking period. This process is an important probe of the electroweak symmetry breaking mechanism in the Standard Model and is sensitive to quartic gauge boson couplings via vector-boson scattering. The fiducial Z(νν¯) γjj cross section for electroweak production is measured to be 0.77−0.30+0.34 fb and is consistent with the Standard Model prediction. Evidence of electroweak Z(νν¯) γjj production is found with an observed significance of 3.2σ for the background-only hypothesis, compared with an expected significance of 3.7σ. The combination of this result with the previously published ATLAS observation of electroweak Z(νν¯) γjj production yields an observed (expected) signal significance of 6.3σ (6.6σ). Limits on anomalous quartic gauge boson couplings are obtained in the framework of effective field theory with dimension-8 operators.
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(2023) Journal of High Energy Physics. 2023, 6, 155. Abstract[All authors]
A search for flavour-changing neutral current (FCNC) tqH interactions involving a top quark, another up-type quark (q = u, c), and a Standard Model (SM) Higgs boson decaying into a τ-lepton pair (H → τ + τ −) is presented. The search is based on a dataset of pp collisions at √s = 13 TeV that corresponds to an integrated luminosity of 139 fb −1 recorded with the ATLAS detector at the Large Hadron Collider. Two processes are considered: single top quark FCNC production in association with a Higgs boson (pp → tH), and top quark pair production in which one of top quarks decays into Wb and the other decays into qH through the FCNC interactions. The search selects events with two hadronically decaying τ-lepton candidates (τ had) or at least one τ had with an additional lepton (e, μ), as well as multiple jets. Event kinematics is used to separate signal from the background through a multivariate discriminant. A slight excess of data is observed with a significance of 2.3σ above the expected SM background, and 95% CL upper limits on the t → qH branching ratios are derived. The observed (expected) 95% CL upper limits set on the t → cH and t → uH branching ratios are 9.4×10−4(4.8−1.4+2.2×10−4) and 6.9×10−4(3.5−1.0+1.5×10−4) , respectively. The corresponding combined observed (expected) upper limits on the dimension-6 operator Wilson coefficients in the effective tqH couplings are Ccφ uφ
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(2023) Journal of High Energy Physics. 2023, 6, 19. Abstract[All authors]
A measurement of the top-quark mass (mt) in the tt¯ → lepton + jets channel is presented, with an experimental technique which exploits semileptonic decays of b-hadrons produced in the top-quark decay chain. The distribution of the invariant mass mℓμ of the lepton, ℓ (with ℓ = e, μ), from the W-boson decay and the muon, μ, originating from the b-hadron decay is reconstructed, and a binned-template profile likelihood fit is performed to extract mt. The measurement is based on data corresponding to an integrated luminosity of 36.1 fb−1 of √s = 13 TeV pp collisions provided by the Large Hadron Collider and recorded by the ATLAS detector. The measured value of the top-quark mass is mt = 174.41 ± 0.39 (stat.) ± 0.66 (syst.) ± 0.25 (recoil) GeV, where the third uncertainty arises from changing the Pythia8 parton shower gluon-recoil scheme, used in top-quark decays, to a recently developed setup. [Figure not available: see fulltext.].
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(2023) Journal of Instrumentation. 18, 6, C06024. Abstract
Time Projection Chambers (TPC)s are excellent tracking detectors for high multiplicity events and can intrinsically be high-rate, but are limited by the ions created in their avalanche stage. GEMs and Micromegas can reduce IBF through their geometry and E͐-field ratios, but these can lead to gain fluctuations and still leave IBF as the dominant source of space charge. An active BPG can block all IBF ions, but their slow drift speed creates too much dead time. A passive BPG will overcome this limitation by using an external B͐-field to allow the electrons to pass through while still blocking all ions. Since the grid changes the electron's trajectory, a loss of resolution will occur. The trajectory is shifted symmetrically along the wires so the wire alignment with respect to the detection pads is a specific question not studied before. We present completed IBF analysis from data collected at Weizmann Institute of Science (WIS), along with an intro to our test on wire resolution.
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(2023) Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 1049, 168017. Abstract[All authors]
We performed feasibility studies for various single transverse spin measurements that are related to the Sivers effect, transversity and the tensor charge, and the Collins fragmentation function. The processes studied include semi-inclusive deep inelastic scattering (SIDIS) where single hadrons (pions and kaons) were detected in addition to the scattered DIS lepton. The data were obtained in PYTHIA6 and GEANT4 simulated e+p collisions at 18 GeV on 275 GeV, 18 on 100, 10 on 100, and 5 on 41 that use the ECCE detector configuration. Typical DIS kinematics were selected, most notably Q2>1GeV2, and cover the x range from 10−4 to 1. The single spin asymmetries were extracted as a function of x and Q2, as well as the semi-inclusive variables z, which corresponds to the momentum fraction the detected hadron carries relative to the struck parton, and PT, which corresponds to the transverse momentum of the detected hadron relative to the virtual photon. They are obtained in azimuthal moments in combinations of the azimuthal angles of the hadron transverse momentum and transverse spin of the nucleon relative to the lepton scattering plane. In order to extract asymmetries, the initially unpolarized MonteCarlo was re-weighted in the true kinematic variables, hadron types and parton flavors based on global fits of fixed target SIDIS experiments and e+e− annihilation data. The expected statistical precision of such measurements is extrapolated to 10 fb−1 and potential systematic uncertainties are approximated given the deviations between true and reconstructed yields. Similar neutron information is obtained by comparing the ECCE e+p pseudo-data with the same from the EIC Yellow Report and scaling the corresponding Yellow Report e+3He pseudo-data uncertainties accordingly. The impact on the knowledge of the Sivers functions, transversity and tensor charges, and the Collins function has then been evaluated in the same phenomenological extractions as in the Yellow Report. The impact is found to be comparable to that obtained with the parametrized Yellow Report detector and shows that the ECCE detector configuration can fulfill the physics goals on these quantities.
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(2023) Journal of High Energy Physics. 2023, 4, 080. Abstract[All authors]
Measurements of single-, double-, and triple-differential cross-sections are presented for boosted top-quark pair-production in 13 TeV protonproton collisions recorded by the ATLAS detector at the LHC. The top quarks are observed through their hadronic decay and reconstructed as large-radius jets with the leading jet having transverse momentum (pT) greater than 500 GeV. The observed data are unfolded to remove detector effects. The particle-level cross-section, multiplied by the tt¯ → WWbb¯ branching fraction and measured in a fiducial phase space defined by requiring the leading and second-leading jets to have pT> 500 GeV and pT> 350 GeV, respectively, is 331 ± 3(stat.) ± 39(syst.) fb. This is approximately 20% lower than the prediction of 398−49+48 fb by Powheg+Pythia 8 with next-to-leading-order (NLO) accuracy but consistent within the theoretical uncertainties. Results are also presented at the parton level, where the effects of top-quark decay, parton showering, and hadronization are removed such that they can be compared with fixed-order next-to-next-to-leading-order (NNLO) calculations. The parton-level cross-section, measured in a fiducial phase space similar to that at particle level, is 1.94 ± 0.02(stat.) ± 0.25(syst.) pb. This agrees with the NNLO prediction of 1.96−0.17+0.02 pb. Reasonable agreement with the differential cross-sections is found for most NLO models, while the NNLO calculations are generally in better agreement with the data. The differential cross-sections are interpreted using a Standard Model effective field-theory formalism and limits are set on Wilson coefficients of several four-fermion operators.
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(2023) Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 1048, 167956. Abstract[All authors]
The EIC Comprehensive Chromodynamics Experiment (ECCE) detector has been recommended as a reference design for the proposed Electron-Ion Collider (EIC) program. This paper presents simulation studies of exclusive J/ψ detection and selected physics impact results in EIC using the projected ECCE detector concept. Exclusive quarkonium photoproduction is one of the most popular processes in EIC, which has a large cross section and a simple final state. Due to the gluonic nature of the exchange Pomeron, this process can be related to the gluon distributions in the nucleus. Preliminary results estimate the excellent statistics benefited from the large cross section of J/ψ photoproduction and superior performance of ECCE detector concept. The precise measurement of exclusive J/ψ photoproduction at EIC will help us to more deeply understand nuclear gluon distributions, near threshold production mechanism and nucleon mass structure.
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(2023) Physical Review D. 107, 5, 052012. Abstract
Polarized proton-proton collisions provide leading-order access to gluons, presenting an opportunity to constrain gluon spin-momentum correlations within transversely polarized protons and enhance our understanding of the three-dimensional structure of the proton. Midrapidity open-heavy-flavor production at s=200 GeV is dominated by gluon-gluon fusion, providing heightened sensitivity to gluon dynamics relative to other production channels. Transverse single-spin asymmetries of positrons and electrons from heavy-flavor hadron decays are measured at midrapidity using the PHENIX detector at the Relativistic Heavy Ion Collider. These charge-separated measurements are sensitive to gluon correlators that can in principle be related to gluon orbital angular momentum via model calculations. Explicit constraints on gluon correlators are extracted for two separate models, one of which had not been constrained previously.
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(2023) Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 1047, 167748. Abstract[All authors]
The Electron-Ion Collider (EIC) is a cutting-edge accelerator facility that will study the nature of the \u201cglue\u201d that binds the building blocks of the visible matter in the universe. The proposed experiment will be realized at Brookhaven National Laboratory in approximately 10 years from now, with detector design and R&D currently ongoing. Notably, EIC is one of the first large-scale facilities to leverage Artificial Intelligence (AI) already starting from the design and R&D phases. The EIC Comprehensive Chromodynamics Experiment (ECCE) is a consortium that proposed a detector design based on a 1.5 T solenoid. The EIC detector proposal review concluded that the ECCE design will serve as the reference design for an EIC detector. Herein we describe a comprehensive optimization of the ECCE tracker using AI. The work required a complex parametrization of the simulated detector system. Our approach dealt with an optimization problem in a multidimensional design space driven by multiple objectives that encode the detector performance, while satisfying several mechanical constraints. We describe our strategy and show results obtained for the ECCE tracking system. The AI-assisted design is agnostic to the simulation framework and can be extended to other sub-detectors or to a system of sub-detectors to further optimize the performance of the EIC detector.
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(2023) Physical Review C. 107, 2, 024914. Abstract
The measurement of direct photons from Au+Au collisions at sNN=39 and 62.4 GeV in the transverse-momentum range 0.4
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(2023) Physical Review C. 107, 2, 024907. Abstract
Recently, the PHENIX Collaboration has published second- and third-harmonic Fourier coefficients v2 and v3 for midrapidity (|η|
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(2023) Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 1047, 167859. Abstract[All authors]
The Electron Ion Collider (EIC) is the next generation of precision QCD facility to be built at Brookhaven National Laboratory in conjunction with Thomas Jefferson National Laboratory. There are a significant number of software and computing challenges that need to be overcome at the EIC. During the EIC detector proposal development period, the ECCE consortium began identifying and addressing these challenges in the process of producing a complete detector proposal based upon detailed detector and physics simulations. In this document, the software and computing efforts to produce this proposal are discussed; furthermore, the computing and software model and resources required for the future of ECCE are described.
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(2023) Acta Physica Polonica B, Proceedings Supplement. 16, 3, 3-A8.1. Abstract
From the first principles, particles with the same quark content and similar masses should have similar kinematic distributions. Transverse mass scaling may be employed to estimate possible differences in the momentum distribution of such particles. Based on this scaling, the excited bottomonium states measured at the LHC are found to be significantly different from Υ(1S) to the extent that the integrated yield of Υ(2S) is 1.6 times less and Υ(3S) 2.4 times less than would be explained by the mass difference. This contribution explains how the estimate is worked out and relates it to other measurements performed at the LHC.
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(2023) Physical review. D. 107, 1, 014012. Abstract
Measurements by the CMS experiment [S. Chatrchyan et al. (CMS Collaboration), J. High Energy Phys. 04 (2014) 103; A. M. Sirunyan et al. (CMS Collaboration), J. High Energy Phys. 11 (2020) 001] reveal a deficit of charged particle tracks in events with higher ϒðnSÞ states. This observation is suggested to be a manifestation of the excited bottomonia suppression in pp interactions. Transverse mass (mT) scaling can be implied to check this assumption in an independent way. The scaling has been observed for a wide range
of particle species in proton-proton collisions at various energies from the SPS to RHIC and the LHC. The observed scaling is known to be different for baryons and mesons, and this work presents a comprehensive study of the mT-scaling of mesons at LHC energies with a focus on heavier mesons. The study demonstrates patterns in the scaling properties of mesons, which are related to the particle quark content. In particular, light species and ground-state quarkonia obey the same scaling, whereas open-flavor particles
deviate from it because their spectra are significantly harder. The magnitude of deviation depends on the flavor of the heaviest quark in the meson. By extending the mT-scaling assumption to the excited bottomonia states, it is observed that the measured cross sections of ϒð2SÞ and ϒð3SÞ are reduced by factors of 1.6 and 2.4 compared to the expectation from the scaling. This observation is consistent with recently observed differences between the event-activity dependence of different ϒðnSÞ meson states. -
(2023) Physical Review C. 107, 1, 014907. Abstract
The PHENIX experiment reports systematic measurements at the Relativistic Heavy Ion Collider of φ-meson production in asymmetric Cu+Au collisions at sNN=200GeV and in U+U collisions at sNN=193GeV. Measurements were performed via the φ→K+K- decay channel at midrapidity |η|
2022
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(2022) Computing and Software for Big Science. 6, 1, 7. Abstract[All authors]
The ATLAS experiment at the Large Hadron Collider has a broad physics programme ranging from precision measurements to direct searches for new particles and new interactions, requiring ever larger and ever more accurate datasets of simulated Monte Carlo events. Detector simulation with Geant4 is accurate but requires significant CPU resources. Over the past decade, ATLAS has developed and utilized tools that replace the most CPU-intensive component of the simulationthe calorimeter shower simulationwith faster simulation methods. Here, AtlFast3, the next generation of high-accuracy fast simulation in ATLAS, is introduced. AtlFast3 combines parameterized approaches with machine-learning techniques and is deployed to meet current and future computing challenges, and simulation needs of the ATLAS experiment. With highly accurate performance and significantly improved modelling of substructure within jets, AtlFast3 can simulate large numbers of events for a wide range of physics processes.
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(2022) Computing and Software for Big Science. 6, 1, 3. Abstract[All authors]
The accurate simulation of additional interactions at the ATLAS experiment for the analysis of protonproton collisions delivered by the Large Hadron Collider presents a significant challenge to the computing resources. During the LHC Run 2 (20152018), there were up to 70 inelastic interactions per bunch crossing, which need to be accounted for in Monte Carlo (MC) production. In this document, a new method to account for these additional interactions in the simulation chain is described. Instead of sampling the inelastic interactions and adding their energy deposits to a hard-scatter interaction one-by-one, the inelastic interactions are presampled, independent of the hard scatter, and stored as combined events. Consequently, for each hard-scatter interaction, only one such presampled event needs to be added as part of the simulation chain. For the Run 2 simulation chain, with an average of 35 interactions per bunch crossing, this new method provides a substantial reduction in MC production CPU needs of around 20%, while reproducing the properties of the reconstructed quantities relevant for physics analyses with good accuracy.
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(2022) European Physical Journal C. 82, 11, 988. Abstract[All authors]
A search for the pair production of heavy leptons as predicted by the type-III seesaw mechanism is presented. The search uses protonproton collision data at a centre-of-mass energy of 13 TeV, corresponding to 139fb-1 of integrated luminosity recorded by the ATLAS detector during Run 2 of the Large Hadron Collider. The analysis focuses on final states with three or four electrons or muons from the possible decays of new heavy leptons via intermediate electroweak bosons. No significant deviations above the Standard Model expectation are observed; upper and lower limits on the heavy lepton production cross-section and masses are derived respectively. These results are then combined for the first time with the ones already published by ATLAS using the channel with two leptons in the final state. The observed lower limit on the mass of the type-III seesaw heavy leptons combining two, three and four lepton channels together is 910 GeV at the 95% confidence level.
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(2022) Physical Review D. 106, 5, 052001. Abstract[All authors]
Searches are performed for nonresonant and resonant di-Higgs boson production in the bb¯γγ final state. The dataset used corresponds to an integrated luminosity of 139 fb-1 of proton-proton collisions at a center-of-mass energy of 13 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. No excess above the expected background is found and upper limits on the di-Higgs boson production cross sections are set. A 95% confidence-level upper limit of 4.2 times the cross section predicted by the Standard Model is set on pp→HH nonresonant production, where the expected limit is 5.7 times the Standard Model predicted value. The expected constraints are obtained for a background hypothesis excluding pp→HH production. The observed (expected) constraints on the Higgs boson trilinear coupling modifier κλ are determined to be [-1.5,6.7] ([-2.4,7.7]) at 95% confidence level, where the expected constraints on κλ are obtained excluding pp→HH production from the background hypothesis. For resonant production of a new hypothetical scalar particle X (X→HH→bb¯γγ), limits on the cross section for pp→X→HH are presented in the narrow-width approximation as a function of mX in the range 251 GeV≤mX≤1000 GeV. The observed (expected) limits on the cross section for pp→X→HH range from 640 fb to 44 fb (391 fb to 46 fb) over the considered mass range.
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(2022) Journal of High Energy Physics. 2022, 8, 104. Abstract[All authors]
A direct search for Higgs bosons produced via vector-boson fusion and subsequently decaying into invisible particles is reported. The analysis uses 139 fb−1 of pp collision data at a centre-of-mass energy of √s = 13 TeV recorded by the ATLAS detector at the LHC. The observed numbers of events are found to be in agreement with the background expectation from Standard Model processes. For a scalar Higgs boson with a mass of 125 GeV and a Standard Model production cross section, an observed upper limit of 0.145 is placed on the branching fraction of its decay into invisible particles at 95% confidence level, with an expected limit of 0.103. These results are interpreted in the context of models where the Higgs boson acts as a portal to dark matter, and limits are set on the scattering cross section of weakly interacting massive particles and nucleons. Invisible decays of additional scalar bosons with masses from 50 GeV to 2 TeV are also studied, and the derived upper limits on the cross section times branching fraction decrease with increasing mass from 1.0 pb for a scalar boson mass of 50 GeV to 0.1 pb at a mass of 2 TeV. [Figure not available: see fulltext.]
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(2022) Physical Review D. 106, 3, 032005. Abstract[All authors]
A search for events with two displaced vertices from long-lived particle (LLP) pairs using data collected by the ATLAS detector at the LHC is presented. This analysis uses 139 fb-1 of proton-proton collision data at √s=13 TeV recorded in 2015-2018. The search employs techniques for reconstructing vertices of LLPs decaying to jets in the muon spectrometer displaced between 3 and 14 m with respect to the primary interaction vertex. The observed numbers of events are consistent with the expected background and limits for several benchmark signals are determined. For the Higgs boson with a mass of 125 GeV, the paper reports the first exclusion limits for branching fractions into neutral long-lived particles below 0.1%, while branching fractions above 10% are excluded at 95% confidence level for LLP proper lifetimes ranging from 4 cm to 72.4 m. In addition, the paper present the first results for the decay of LLPs into tt¯ in the ATLAS muon spectrometer.
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(2022) Journal of High Energy Physics. 2022, 8, 089. Abstract[All authors]
This paper presents updated Monte Carlo configurations used to model the production of single electroweak vector bosons (W, Z/γ∗) in association with jets in proton-proton collisions for the ATLAS experiment at the Large Hadron Collider. Improvements pertaining to the electroweak input scheme, parton-shower splitting kernels and scale-setting scheme are shown for multi-jet merged configurations accurate to next-to-leading order in the strong and electroweak couplings. The computational resources required for these set-ups are assessed, and approximations are introduced resulting in a factor three reduction of the per-event CPU time without affecting the physics modelling performance. Continuous statistical enhancement techniques are introduced by ATLAS in order to populate low cross-section regions of phase space and are shown to match or exceed the generated effective luminosity. This, together with the lower per-event CPU time, results in a 50% reduction in the required computing resources compared to a legacy set-up previously used by the ATLAS collaboration. The set-ups described in this paper will be used for future ATLAS analyses and lay the foundation for the next generation of Monte Carlo predictions for single vector-boson plus jets production.
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(2022) European Physical Journal C. 82, 8, 717. Abstract[All authors]
A search for the Higgs boson decaying into a pair of charm quarks is presented. The analysis uses protonproton collisions to target the production of a Higgs boson in association with a leptonically decaying W or Z boson. The dataset delivered by the LHC at a centre-of-mass energy of √s=13TeV and recorded by the ATLAS detector corresponds to an integrated luminosity of 139 fb-1. Flavour-tagging algorithms are used to identify jets originating from the hadronisation of charm quarks. The analysis method is validated with the simultaneous measurement of WW, WZ and ZZ production, with observed (expected) significances of 2.6 (2.2) standard deviations above the background-only prediction for the (W/ Z) Z(→ cc¯) process and 3.8 (4.6) standard deviations for the (W/ Z) W(→ cq) process. The (W/ Z) H(→ cc¯) search yields an observed (expected) upper limit of 26 (31) times the predicted Standard Model cross-section times branching fraction for a Higgs boson with a mass of 125GeV, corresponding to an observed (expected) constraint on the charm Yukawa coupling modifier |κc|
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(2022) Physical Review D. 106, 3, 032008. Abstract[All authors]
Several observables sensitive to the fragmentation of b quarks into b hadrons are measured using 36 fb-1 of √s=13 TeV proton-proton collision data collected with the ATLAS detector at the LHC. Jets containing b hadrons are obtained from a sample of dileptonic t¯t events, and the associated set of charged-particle tracks is separated into those from the primary pp interaction vertex and those from the displaced b-decay secondary vertex. This division is used to construct observables that characterize the longitudinal and transverse momentum distributions of the b hadron within the jet. The measurements have been corrected for detector effects and provide a test of heavy-quark-fragmentation modeling at the LHC in a system where the top-quark decay products are color connected to the proton beam remnants. The unfolded distributions are compared with the predictions of several modern Monte Carlo parton-shower generators and generator tunes, and a wide range of agreement with the data is observed, with p values varying from 5×10-4 to 0.98. These measurements complement similar measurements from e+e- collider experiments in which the b quarks originate from a color singlet Z/γ∗.
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(2022) Physical Review C. 106, 1, 014908. Abstract
Small nuclear collisions are mainly sensitive to cold-nuclear-matter effects; however, the collective behavior observed in these collisions shows a hint of hot-nuclear-matter effects. The identified-particle spectra, especially the φ mesons which contain strange and antistrange quarks and have a relatively small hadronic-interaction cross section, are a good tool to study these effects. The PHENIX experiment has measured φ mesons in a specific set of small collision systems p+Al, p+Au, and He3+Au, as well as d+Au [Adare, Phys. Rev. C 83, 024909 (2011)0556-281310.1103/PhysRevC.83.024909], at sNN=200 GeV. The transverse-momentum spectra and nuclear-modification factors are presented and compared to theoretical-model predictions. The comparisons with different calculations suggest that quark-gluon plasma may be formed in these small collision systems at sNN=200 GeV. However, the volume and the lifetime of the produced medium may be insufficient for observing strangeness-enhancement and jet-quenching effects. The comparison with calculations suggests that the main production mechanisms of φ mesons at midrapidity may be different in p+Al versus p/d/He3+Au collisions at sNN=200 GeV. While thermal quark recombination seems to dominate in p/d/He3+Au collisions, fragmentation seems to be the main production mechanism in p+Al collisions.
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(2022) Physical Review C. 105, 6, 064902. Abstract
The PHENIX Collaboration presents a systematic study of inclusive π0 production from p+p, p+Al, p+Au, d+Au, and He3+Au collisions at sNN=200GeV. Measurements were performed with different centrality selections as well as the total inelastic, 0-100%, selection for all collision systems. For 0-100% collisions, the nuclear-modification factors, RxA, are consistent with unity for pT above 8GeV/c, but exhibit an enhancement in peripheral collisions and a suppression in central collisions. The enhancement and suppression characteristics are similar for all systems for the same centrality class. It is shown that for high-pT-π0 production, the nucleons in the d and He3 interact mostly independently with the Au nucleus and that the counterintuitive centrality dependence is likely due to a physical correlation between multiplicity and the presence of a hard scattering process. These observations disfavor models where parton energy loss has a significant contribution to nuclear modifications in small systems. Nuclear modifications at lower pT resemble the Cronin effect - an increase followed by a peak in central or inelastic collisions and a plateau in peripheral collisions. The peak height has a characteristic ordering by system size as p+Au>d+Au>He3+Au>p+Al. For collisions with Au ions, current calculations based on initial-state cold nuclear matter effects result in the opposite order, suggesting the presence of other contributions to nuclear modifications, in particular at lower pT.
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(2022) Journal of High Energy Physics. 2022, 6, 097. Abstract[All authors]
The associated production of a Higgs boson and a top-quark pair is measured in events characterised by the presence of one or two electrons or muons. The Higgs boson decay into a b-quark pair is used. The analysed data, corresponding to an integrated luminosity of 139 fb−1, were collected in proton-proton collisions at the Large Hadron Collider between 2015 and 2018 at a centre-of-mass energy of √s = 13 TeV. The measured signal strength, defined as the ratio of the measured signal yield to that predicted by the Standard Model, is 0.35−0.34+0.36. This result is compatible with the Standard Model prediction and corresponds to an observed (expected) significance of 1.0 (2.7) standard deviations. The signal strength is also measured differentially in bins of the Higgs boson transverse momentum in the simplified template cross-section framework, including a bin for specially selected boosted Higgs bosons with transverse momentum above 300 GeV.
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(2022) Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. 829, 137066. Abstract[All authors]
A search for invisible decays of the Higgs boson as well as searches for dark matter candidates, produced together with a leptonically decaying Z boson, are presented. The analysis is performed using proton−proton collisions at a centre-of-mass energy of 13 TeV, delivered by the LHC, corresponding to an integrated luminosity of 139 fb−1 and recorded by the ATLAS experiment. Assuming Standard Model cross-sections for ZH production, the observed (expected) upper limit on the branching ratio of the Higgs boson to invisible particles is found to be 19% (19%) at the 95% confidence level. Exclusion limits are also set for simplified dark matter models and two-Higgs-doublet models with an additional pseudoscalar mediator.
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(2022) Physical Review C. 105, 6, 064912. Abstract
Suppression of the J/ψ nuclear-modification factor has been seen as a trademark signature of final-state effects in large collision systems for decades. In small systems, the nuclear modification was attributed to cold-nuclear-matter effects until the observation of strong differential suppression of the ψ(2S) state in p+A and d+A collisions suggested the presence of final-state effects. Results of J/ψ and ψ(2S) measurements in the dimuon decay channel are presented here for p+p, p+Al, and p+Au collision systems at sNN=200GeV. The results are predominantly shown in the form of the nuclear-modification factor, RpA, the ratio of the ψ(2S) invariant yield per nucleon-nucleon collision in collisions of proton on target nucleus to that in p+p collisions. Measurements of the J/ψ and ψ(2S) nuclear-modification factor are compared with shadowing and transport-model predictions, as well as to complementary measurements at Large Hadron Collider energies.
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(2022) Physical Review D. 105, 3, 032004. Abstract
In 2015 the PHENIX collaboration at the Relativistic Heavy Ion Collider recorded p+p, p+Al, and p+Au collision data at center of mass energies of sNN=200 GeV with the proton beam(s) transversely polarized. At very forward rapidities η>6.8 relative to the polarized proton beam, neutrons were detected either inclusively or in (anti)correlation with detector activity related to hard collisions. The resulting single spin asymmetries, that were previously reported, have now been extracted as a function of the transverse momentum of the neutron as well as its longitudinal momentum fraction xF. The explicit kinematic dependence, combined with the correlation information allows for a closer look at the interplay of different mechanisms suggested to describe these asymmetries, such as hadronic interactions or electromagnetic interactions in ultraperipheral collisions, UPC. Events that are correlated with a hard collision indeed display a mostly negative asymmetry that increases in magnitude as a function of transverse momentum with only little dependence on xF. In contrast, events that are not likely to have emerged from a hard collision display positive asymmetries for the nuclear collisions with a kinematic dependence that resembles that of a UPC based model. Because the UPC interaction depends strongly on the charge of the nucleus, those effects are very small for p+p collisions, moderate for p+Al collisions, and large for p+Au collisions.
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(2022) Physical Review D. 105, 3, 032003. Abstract
In 2015, the PHENIX Collaboration has measured single-spin asymmetries for charged pions in transversely polarized p+p collisions at the center-of-mass energy of s=200 GeV. The pions were detected at central rapidities of |η|
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(2022) Physical Review C. 105, 2, 024901. Abstract
There is strong evidence for the formation of small droplets of quark-gluon plasma in p/d/He3+Au collisions at the Relativistic Heavy Ion Collider (RHIC) and in p+p/Pb collisions at the Large Hadron Collider. In particular, the analysis of data at RHIC for different geometries obtained by varying the projectile size and shape has proved insightful. In the present analysis, we find excellent agreement with the previously published PHENIX at RHIC results on elliptical and triangular flow with an independent analysis via the two-particle correlation method, which has quite different systematic uncertainties and an independent code base. In addition, the results are extended to other detector combinations with different kinematic (pseudorapidity) coverage. These results provide additional constraints on contributions from nonflow and longitudinal decorrelations.
2021
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(2021) Physical review letters. 127, 16, 162001. Abstract
Studying spin-momentum correlations in hadronic collisions offers a glimpse into a three-dimensional picture of proton structure. The transverse single-spin asymmetry for midrapidity isolated direct photons in collisions at is measured with the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC). Because direct photons in particular are produced from the hard scattering and do not interact via the strong force, this measurement is a clean probe of initial-state spin-momentum correlations inside the proton and is in particular sensitive to gluon interference effects within the proton. This is the first time direct photons have been used as a probe of spin-momentum correlations at RHIC. The uncertainties on the results are a 50-fold improvement with respect to those of the one prior measurement for the same observable, from the Fermilab E704 experiment. These results constrain gluon spin-momentum correlations in transversely polarized protons.
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(2021) Physical Review D. 103, 5, 052009. Abstract
We present a measurement of the transverse single-spin asymmetry for π0 and η mesons in p↑+p collisions in the pseudorapidity range |η|
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(2021) Physical Review D - Particles, Fields, Gravitation and Cosmology. 103, 3, 032007. Abstract[All authors]
In 2015, the PHENIX collaboration has measured very forward (η>6.8) single spin asymmetries of inclusive neutrons in transversely polarized proton-proton and proton-nucleus collisions at a center of mass energy of 200 GeV. A previous publication from this dataset concentrated on the nuclear dependence of such asymmetries. In this measurement the explicit transverse momentum dependence of inclusive neutron single spin asymmetries for proton-proton collisions is extracted using a bootstrapping unfolding technique on the transverse momenta. This explicit transverse momentum dependence will help improve the understanding of the mechanisms that create these asymmetries.
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(2021) IEEE Transactions on Nuclear Science. 68, 1, p. 59-69 Abstract
The ion backflow (IBF) is the main limiting factor for operating time projection chambers (TPCs) at high event rates. A significant effort is invested by many experimental groups to solve this problem. This article explores a solution based on operating a passive bipolar wire grid. In the presence of the magnetic field, the grid more effectively attenuates the ion current than the electron current going through it. Transparencies of the grid to electrons and ions are measured for different gas mixtures and magnitudes of the magnetic field. The results suggest that in a sufficiently strong magnetic field, the bipolar wire grid can be used as an effective and independent device to suppress the IBF in TPCs.
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(2021) Journal of High Energy Physics. 2021, 1, 188. Abstract[All authors]
A measurement of event-shape variables in proton-proton collisions at large momentum transfer is presented using data collected at s = 13 TeV with the ATLAS detector at the Large Hadron Collider. Six event-shape variables calculated using hadronic jets are studied in inclusive multijet events using data corresponding to an integrated luminosity of 139 fb−1. Measurements are performed in bins of jet multiplicity and in different ranges of the scalar sum of the transverse momenta of the two leading jets, reaching scales beyond 2 TeV. These measurements are compared with predictions from Monte Carlo event generators containing leading-order or next-to-leading order matrix elements matched to parton showers simulated to leading-logarithm accuracy. At low jet multiplicities, shape discrepancies between the measurements and the Monte Carlo predictions are observed. At high jet multiplicities, the shapes are better described but discrepancies in the normalisation are observed. [Figure not available: see fulltext.]
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(2021) Physics Letters B. 812, 135980. Abstract[All authors]
A search for the dimuon decay of the Standard Model (SM) Higgs boson is performed using data corresponding to an integrated luminosity of 139 fb(-1) collected with the ATLAS detector in Run 2 pp collisions at root s = 13 TeV at the Large Hadron Collider. The observed (expected) significance over the background-only hypothesis for a Higgs boson with a mass of 125.09 GeV is 2.0 sigma (1.7 sigma). The observed upper limit on the cross section times branching ratio for pp -> H -> mu mu is 2.2 times the SM prediction at 95% confidence level, while the expected limit on a H -> mu mu signal assuming the absence (presence) of a SM signal is 1.1(2.0). The best-fit value of the signal strength parameter, defined as the ratio of the observed signal yield to the one expected in the SM, is mu = 1.2 +/- 0.6.
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(2021) Physics Letters B. 812, 135991. Abstract[All authors]
The integrated fiducial cross-section and unfolded differential jet mass spectrum of high transverse momentum Z -> b (b) over bar decays are measured in Z gamma events in proton-proton collisions at root s = 13 TeV. The data analysed were collected between 2015 and 2016 with the ATLAS detector at the Large Hadron Collider and correspond to an integrated luminosity of 36.1 fb(-1). Photons are required to have a transverse momentum p(T) > 175 GeV. The Z -> b (b) over bar decay is reconstructed using a jet with p(T) > 200 GeV, found with the anti-k(t) R = 1.0 jet algorithm, and groomed to remove soft and wide-angle radiation and to mitigate contributions from the underlying event and additional proton-proton collisions. Two different but related measurements are performed using two jet grooming definitions for reconstructing the Z -> b (b) over bar decay: trimming and soft drop. These algorithms differ in their experimental and phenomenological implications regarding jet mass reconstruction and theoretical precision. To identify Zbosons, b-tagged R = 0.2 track-jets matched to the groomed large-R calorimeter jet are used as a proxy for the b-quarks. The signal yield is determined from fits of the data-driven background templates to the different jet mass distributions for the two grooming methods. Integrated fiducial cross-sections and unfolded jet mass spectra for each grooming method are compared with leading-order theoretical predictions. The results are found to be in good agreement with Standard Model expectations within the current statistical and systematic uncertainties.
2020
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(2020) Physical Review C. 102, 6, 064905. Abstract
The PHENIX experiment at the Relativistic Heavy Ion Collider measured π0 and η mesons at midrapidity in U+U collisions at sNN=192 GeV in a wide transverse momentum range. Measurements were performed in the π0(η)→γγ decay modes. A strong suppression of π0 and η meson production at high transverse momentum was observed in central U+U collisions relative to binary scaled p+p results. Yields of π0 and η mesons measured in U+U collisions show similar suppression pattern to those measured in Au+Au collisions at sNN=200 GeV for similar numbers of participant nucleons. The η/π0 ratios do not show dependence on centrality or transverse momentum and are consistent with previously measured values in hadron-hadron, hadron-nucleus, nucleus-nucleus, and e+e- collisions.
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(2020) Physical Review C. 102, 5, 054910. Abstract
We present direct photon-hadron correlations in 200 GeV/A Au+Au, d+Au, and p+p collisions, for direct photon pT from 5-12 GeV/c, collected by the PHENIX Collaboration in the years from 2006 to 2011. We observe no significant modification of jet fragmentation in d+Au collisions, indicating that cold nuclear matter effects are small or absent. Hadrons carrying a large fraction of the quark's momentum are suppressed in Au+Au compared to p+p and d+Au. As the momentum fraction decreases, the yield of hadrons in Au+Au increases to an excess over the yield in p+p collisions. The excess is at large angles and at low hadron pT and is most pronounced for hadrons associated with lower momentum direct photons. Comparison to theoretical calculations suggests that the hadron excess arises from medium response to energy deposited by jets.
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(2020) Physical review D. 102, 9, 092002. Abstract
The cross section of bottom quark-antiquark (bb¯) production in p+p collisions at s=510 GeV is measured with the PHENIX detector at the Relativistic Heavy Ion Collider. The results are based on the yield of high mass, like-sign muon pairs measured within the PHENIX muon arm acceptance (1.2
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(2020) Physical Review D. 102, 7, 072008. Abstract
The PHENIX experiment has measured the spin alignment for inclusive J/ψ→e+e- decays in proton-proton collisions at s=510 GeV at midrapidity. The angular distributions have been measured in three different polarization frames, and the three decay angular coefficients have been extracted in a full two-dimensional analysis. Previously, PHENIX saw large longitudinal net polarization at forward rapidity at the same collision energy. This analysis at midrapidity, complementary to the previous PHENIX results, sees no sizable polarization in the measured transverse momentum range of 0.0
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(2020) Physical Review D. 102, 3, 032001. Abstract
The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the longitudinal double spin asymmetries, A(LL), for charged pions at midrapidity (vertical bar eta vertical bar
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(2020) Physical Review C. 102, 1, 014902. Abstract
Charmonium is a valuable probe in heavy-ion collisions to study the properties of the quark gluon plasma, and is also an interesting probe in small collision systems to study cold nuclear matter effects, which are also present in large collision systems. With the recent observations of collective behavior of produced particles in small system collisions, measurements of the modification of charmonium in small systems have become increasingly relevant. We present the results of J/Psi measurements at forward and backward rapidity in various small collision systems, p + p, p + Al, p + Au, and He-3+Au, at root s(NN) = 200 GeV. The results are presented in the form of the observable RAB, the nuclear modification factor, a measure of the ratio of the J/Psi invariant yield compared to the scaled yield in p + p collisions. We examine the rapidity, transverse momentum, and collision centrality dependence of nuclear effects on J/Psi production with different projectile sizes p and He-3, and different target sizes Al and Au. The modification is found to be strongly dependent on the target size, but to be very similar for p + Au and He-3+Au. However, for 0%-20% central collisions at backward rapidity, the modification factor for He-3+Au is found to be smaller than that for p + Au, with a mean fit to the ratio of 0.89 +/- 0.03(stat)+/- 0.08(syst), possibly indicating final state effects due to the larger projectile size.
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(2020) 2019 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC). Abstract
Time Projection Chamber (TPC) is one of the main tracking systems for many current and future collider experiments at RHIC and LHC. It has a capability to measure the space points of charged tracks for good momentum resolution as well as the energy loss (dE/dx) for particle identification with good energy resolution. Both of these features depend strongly on the amount of space charge in the TPC gas volume, mainly due to the ions from the amplification stage. An active gating grid has been used thus far to gate the electrons and ions by switching the polarities of the grid wires. Therefore, active gating does introduce a limitation for data taking rates in high luminosity collisions. In this work we propose several options of a passive gating, where a significant reduction of Ion Back Flow (IBF) is possible in a high luminosity environment without any dead time issues due to gating operation. Particularly, the application of a TPC passive gating for the sPHENIX experiment at RHIC is presented, which is currently under development.
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(2020) Physical Review C. 101, 3, 034910. Abstract
The PHENIX experiment has studied nuclear effects in p + Al and p + Au collisions at root S-NN = 200GeV on charged hadron production at forward rapidity (1.4
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(2020) Physical Review D. 101, 5, 052006. Abstract
The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the differential cross section, mean transverse momentum, mean transverse momentum squared of inclusive J/psi, and cross section ratio of psi(2S) to J/psi at forward rapidity in p + p collisions at root s = 510 GeV via the dimuon decay channel. Comparison is made to inclusive J/psi cross sections measured at root s = 200 GeV and 2.76-13 TeV. The result is also compared to leading-order nonrelativistic QCD calculations coupled to a color-glass-condensate description of the low-x gluons in the proton at low transverse momentum (p(T)) and to next-to-leading order nonrelativistic QCD calculations for the rest of the p(T) range. These calculations overestimate the data at low p(T). While consistent with the data within uncertainties above approximate to 3 GeV/c, the calculations are systematically below the data. The total cross section times the branching ratio is BR d sigma(J/)(psi)(pp) / dy(1.2
2019
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(2019) Physical Review Letters. 123, 12, 122001. Abstract
We report on the nuclear dependence of transverse single-spin asymmetries (TSSAs) in the production of positively charged hadrons in polarized p(up arrow) + p, p(up arrow) + Al, and p(up arrow) + Au collisions at root s(NN) = 200 GeV. The measurements have been performed at forward rapidity (1.4
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(2019) Physical Review Letters. 123, 2, 022301. Abstract
The PHENIX collaboration presents first measurements of low-momentum (0.4 5 GeV= c), but when results from different collision energies are compared, an additional root s(NN) -dependent multiplicative factor is needed to describe the integrated-direct-photon yield.
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(2019) Physical Review C. 99, 5, 054903. Abstract
We present measurements of azimuthal correlations of charged hadron pairs in sNN=200 GeV Au+Au collisions for the trigger and associated particle transverse-momentum ranges of 1
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(2019) Physical Review D. 99, 9, 092003. Abstract
Measurements of the differential production of electrons from open-heavy-flavor hadrons with charm-and bottom-quark content in p + p collisions at root s = 200 GeV are presented. The measurements proceed through displaced-vertex analyses of electron tracks from the semileptonic decay of charm and bottom hadrons using the PHENIX silicon-vertex detector. The relative contribution of electrons from bottom decays to inclusive heavy-flavor-electron production is found to be consistent with fixed-order-plus-next-to-leading-log perturbative-QCD calculations within experimental and theoretical uncertainties. These new measurements in p + p collisions provide a precision baseline for comparable forthcoming measurements in A + A collisions.
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(2019) Physical Review D. 99, 7, 072003. Abstract
PHENIX reports differential cross sections of μμ pairs from semileptonic heavy-flavor decays and the Drell-Yan production mechanism measured in p+p collisions at s=200 GeV at forward and backward rapidity (1.2
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(2019) Nature Physics. 15, 3, p. 214-220 Abstract
Experimental studies of the collisions of heavy nuclei at relativistic energies have established the properties of the quark-gluon plasma (QGP), a state of hot, dense nuclear matter in which quarks and gluons are not bound into hadrons(1-4). In this state, matter behaves as a nearly inviscid fluid(5) that efficiently translates initial spatial anisotropies into correlated momentum anisotropies among the particles produced, creating a common velocity field pattern known as collective flow. In recent years, comparable momentum anisotropies have been measured in small-system proton-proton (p+p) and proton-nucleus (p+A) collisions, despite expectations that the volume and lifetime of the medium produced would be too small to form a QGP. Here we report on the observation of elliptic and triangular flow patterns of charged particles produced in proton-gold (p+Au), deuteron-gold (d+Au) and helium-gold (He-3+Au) collisions at a nucleon-nucleon centre-of-mass energy root s(NN) = 200 GeV. The unique combination of three distinct initial geometries and two flow patterns provides unprecedented model discrimination. Hydrodynamical models, which include the formation of a short-lived QGP droplet, provide the best simultaneous description of these measurements.
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(2019) Nuclear Physics A. 982, p. 955-958 Abstract
The sPHENIX experiment at RHIC will collect high statistics proton-proton, proton-nucleus and nucleus-nucleus data, starting in the early 2020's. The sPHENIX capabilities enable state-of-the-art studies of jet modification, upsilon suppression and open heavy flavor production to probe the microscopic nature of the strongly-coupled Quark Gluon Plasma, and will allow a broad range of cold QCD studies. The sPHENIX detector will provide precision vertexing, tracking and electromagnetic and hadronic calorimetry in the central pseudorapidity region vertical bar eta vertical bar
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(2019) PHYSICAL REVIEW C. 99, 2, 024903. Abstract
We present measurements of elliptic and triangular azimuthal anisotropy of charged particles detected at forward rapidity 1
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(2019) Nuclear Physics A. 982, p. 275-278 Abstract[All authors]
Forward hadron measurements in p(d)+A provide a signal to study nuclear shadowing, initial state energy loss and/or gluon saturation effects as a function of rapidity, centrality and energy. High p
T identified π
0 measurements are an essential first step toward measuring prompt photon production. The π
0 measurements are enabled by the PHENIX MPC-EX detector, a Si-W preshower detector located in front of the Muon Piston Calorimeter (MPC), expanding the neutral pion reconstruction capabilities in the rapidity range 3.1 NN=200,62,39and19.6GeV; and p+p and p+Au(Al) data with the FVTX in 2015 at 200 GeV. In this talk, we will present first results for high p
T π
0 production from the s
NN=200GeV dataset, the status of the prompt photon measurement, as well as charged hadron nuclear modification factors in p+Au(Al) and
3He+Au. -
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2018
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(2018) European Physical Journal C. 78, 12, 995. Abstract[All authors]
A search for the electroweak production of charginos, neutralinos and sleptons decaying into final states involving two or three electrons or muons is presented. The analysis is based on 36.1 fb−1 of √s = 13 TeV proton proton collisions recorded by the ATLAS detector at the Large Hadron Collider. Several scenarios based on simplified models are considered. These include the associated production of the next-to-lightest neutralino and the lightest chargino, followed by their decays into final states with leptons and the lightest neutralino via either sleptons or Standard Model gauge bosons; direct production of chargino pairs, which in turn decay into leptons and the lightest neutralino via intermediate sleptons; and slepton pair production, where each slepton decays directly into the lightest neutralino and a lepton. No significant deviations from the Standard Model expectation are observed and stringent limits at 95% confidence level are placed on the masses of relevant supersymmetric particles in each of these scenarios. For a massless lightest neutralino, masses up to 580 GeV are excluded for the associated production of the next-to-lightest neutralino and the lightest chargino, assuming gauge-boson mediated decays, whereas for slepton-pair production masses up to 500 GeV are excluded assuming three generations of mass-degenerate sleptons.
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(2018) Physical Review Letters. 121, 22, 222301. Abstract
Asymmetric nuclear collisions of p + Al, p + Au, d + Au, and He-3 + Au at root S-NN = 200 GeV provide an excellent laboratory for understanding particle production, as well as exploring interactions among these particles after their initial creation in the collision. We present measurements of charged hadron production dN(ch)/d eta in all such collision systems over a broad pseudorapidity range and as a function of collision multiplicity. A simple wounded quark model is remarkably successful at describing the full data set. We also measure the elliptic flow 12 over a similarly broad pseudorapidity range. These measurements provide key constraints on models of particle emission and their translation into flow.
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(2018) Physical Review D. 98, 9, 092006. Abstract
The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the differential cross section of phi(1020)-meson production at forward rapidity in p + p collisions at root s = 510 GeV via the dimuon decay channel. The partial cross section in the rapidity and P-T ranges 1.2
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(2018) Physical Review D. 98, 7, 072004. Abstract
Dihadron and isolated direct photon-hadron angular correlations are measured in p + p collisions at root s = 200 GeV. The correlations are sensitive to nonperturbative initial-state and final-state transverse momenta k(T) and j(T) in the azimuthal nearly back-to-back region. Delta phi similar to pi. To have sensitivity to small transverse momentum scales, nonperturbative momentum widths of pout, the out-of-plane transversemomentum component perpendicular to the trigger particle, are measured. In this region, the evolution of pout can be studied when several different hard scales are measured. These widths are used to investigate possible effects from transverse-momentum-dependent factorization breaking. When accounting for the longitudinal-momentum fraction of the away-side hadron with respect to the near-side trigger particle, the widths are found to increase with the hard scale; this is qualitatively similar to the observed behavior in Drell-Yan and semi-inclusive deep-inelastic scattering interactions, where factorization is predicted to hold. The momentum widths are also studied as a function of center-of-mass energy by comparing to previous measurements at root s = 510 GeV. The nonperturbative jet widths also appear to increase with root s at a similar x(T), which is qualitatively consistent to similar measurements in Drell-Yan interactions. Future detailed global comparisons between measurements of processes where transverse-momentum-dependent factorization is predicted to hold and be broken will provide further insight into the role of color in hadronic interactions.
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(2018) Physical Review D. 98, 3, 032007. Abstract[All authors]
We have measured the cross section and single-spin asymmetries from forward W-+/- -> mu(+/-)nu production in longitudinally polarized p + p collisions at root s = 510 GeV using the PHENIX detector at the Relativistic Heavy Ion Collider. The cross sections are consistent with previous measurements at this collision energy, while the most forward and backward longitudinal single spin asymmetries provide new insights into the sea quark helicities in the proton. The charge of the W bosons provides a natural flavor separation of the participating partons.
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(2018) PHYSICAL REVIEW C. 98, 1, 014912. Abstract
We present measurements of two-particle angular correlations between high-transverse-momentum (2
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(2018) Physical Review D. 98, 1, 012006. Abstract[All authors]
We report the transverse single-spin asymmetries of J/psi production at forward and backward rapidity, 1.2
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(2018) PHYSICAL REVIEW C. 97, 6, 064904. Abstract
We present measurements of the transverse-momentum dependence of elliptic flow upsilon(2) for identified pions and (anti)protons at midrapidity (vertical bar eta vertical bar
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(2018) PHYSICAL REVIEW C. 97, 6, 064911. Abstract
We present a detailed measurement of charged two-pion correlation functions in 0-30% centrality root= 200 GeV Au+Au collisions by the PHENIX experiment at the Relativistic Heavy Ion Collider. The data are well described by Bose-Einstein correlation functions stemming from Levy-stable source distributions. Using a fine transverse momentum binning, we extract the correlation strength parameter lambda, the Levy index of stability alpha, and the Levy length scale parameter R as a function of average transverse mass of the parr m(T). We find that the positively and the negatively charged pion pairs yield consistent results, and their correlation functions are represented, within uncertainties, by the same Levy-stable source functions. The lambda(m(T)) measurements indicate a decrease of the strength of the correlations at low m(T). The Levy length scale parameter R(m(T)) decreases with increasing m(T), following a hydrodynamically predicted type of scaling behavior. The values of the Levy index of stability a are found to be significantly lower than the Gaussian case of alpha = 2, but also significantly larger than the conjectured value that may characterize the critical point of a second-order quark-hadron phase transition.
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(2018) Physical Review Letters. 120, 6, 062302. Abstract
Recently, multiparticle-correlation measurements of relativistic p/d/He3+Au, p+Pb, and even p+p collisions show surprising collective signatures. Here, we present beam-energy-scan measurements of two-, four-, and six-particle angular correlations in d+Au collisions at sNN=200, 62.4, 39, and 19.6 GeV. We also present measurements of two- and four-particle angular correlations in p+Au collisions at sNN=200 GeV. We find the four-particle cumulant to be real valued for d+Au collisions at all four energies. We also find that the four-particle cumulant in p+Au has the opposite sign as that in d+Au. Further, we find that the six-particle cumulant agrees with the four-particle cumulant in d+Au collisions at 200 GeV, indicating that nonflow effects are subdominant. These observations provide strong evidence that the correlations originate from the initial geometric configuration, which is then translated into the momentum distribution for all particles, commonly referred to as collectivity.
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(2018) Physical Review Letters. 120, 2, 022001. Abstract
During 2015, the Relativistic Heavy Ion Collider (RHIC) provided collisions of transversely polarized protons with Au and Al nuclei for the first time, enabling the exploration of transverse-single-spin asymmetries with heavy nuclei. Large single-spin asymmetries in very forward neutron production have been previously observed in transversely polarized p+p collisions at RHIC, and the existing theoretical framework that was successful in describing the single-spin asymmetry in p+p collisions predicts only a moderate atomic-mass-number (A) dependence. In contrast, the asymmetries observed at RHIC in p+A collisions showed a surprisingly strong A dependence in inclusive forward neutron production. The observed asymmetry in p+Al collisions is much smaller, while the asymmetry in p+Au collisions is a factor of 3 larger in absolute value and of opposite sign. The interplay of different neutron production mechanisms is discussed as a possible explanation of the observed A dependence.
2017
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(2017) PHYSICAL REVIEW C. 96, 6, 064901. Abstract[All authors]
The fraction of J/ψ mesons which come from B-meson decay, FB→J/ψ, is measured for J/ψ rapidity 1.2
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(2017) PHYSICAL REVIEW C. 96, 6, 064905. Abstract[All authors]
We present measurements of the elliptic flow (v2) as a function of transverse momentum (pT), pseudorapidity (η), and centrality in d+Au collisions at sNN=200, 62.4, 39, and 19.6 GeV. The beam-energy scan of d+Au collisions provides a testing ground for the onset of flow signatures in small collision systems. We measure a nonzero v2 signal at all four collision energies, which, at midrapidity and low pT, is consistent with predictions from viscous hydrodynamic models. Comparisons with calculations from parton transport models (based on the ampt Monte Carlo generator) show good agreement with the data at midrapidity to forward (d-going) rapidities and low pT. At backward (Au-going) rapidities and pT>1.5GeV/c, the data diverges from ampt calculations of v2 relative to the initial geometry, indicating the possible dominance of nongeometry related correlations, referred to as nonflow. We also present measurements of the charged-particle multiplicity (dNch/dη) as a function of η in central d+Au collisions at the same energies. We find that in d+Au collisions at sNN=200 GeV the v2 scales with dNch/dη over all η in the PHENIX acceptance. At sNN=62.4, and 39 GeV, v2 scales with dNch/dη at midrapidity and forward rapidity, but falls off at backward rapidity. This departure from the dNch/dη scaling may be a further indication of nonflow effects dominating at backward rapidity.
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(2017) Journal of High Energy Physics. 2017, 11, 86. Abstract[All authors]
The cross section of a top-quark pair produced in association with a photon is measured in proton-proton collisions at a centre-of-mass energy of s=8 TeV with 20.2 fb−1 of data collected by the ATLAS detector at the Large Hadron Collider in 2012. The measurement is performed by selecting events that contain a photon with transverse momentum pT > 15 GeV, an isolated lepton with large transverse momentum, large missing transverse momentum, and at least four jets, where at least one is identified as originating from a b-quark. The production cross section is measured in a fiducial region close to the selection requirements. It is found to be 139 ± 7 (stat.) ± 17 (syst.) fb, in good agreement with the theoretical prediction at next-to-leading order of 151 ± 24 fb. In addition, differential cross sections in the fiducial region are measured as a function of the transverse momentum and pseudorapidity of the photon.[Figure not available: see fulltext.].
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(2017) PHYSICAL REVIEW C. 96, 2, 024907. Abstract[All authors]
We report a measurement of e+e- pairs from semileptonic heavy-flavor decays in p+p collisions at sNN=200 GeV. The e+e- pair yield from bb and cc is separated by exploiting a double differential fit done simultaneously in dielectron invariant mass and pT. We used three different event generators, pythia, mc@nlo, and powheg, to simulate the e+e- spectra from cc and bb production. The data can be well described by all three generators within the detector acceptance. However, when using the generators to extrapolate to 4π, significant differences are observed for the total cross section. These difference are less pronounced for bb than for cc. The same model dependence was observed in already published d+A data. The p+p data are also directly compared with d+A data in mass and pT, and within the statistical accuracy no nuclear modification is seen.
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(2017) Physical Review D - Particles, Fields, Gravitation and Cosmology. 95, 11, 112001. Abstract
The cross section and transverse single-spin asymmetries of μ- and μ+ from open heavy-flavor decays in polarized p+p collisions at s=200 GeV were measured by the PHENIX experiment during 2012 at the Relativistic Heavy Ion Collider. Because heavy-flavor production is dominated by gluon-gluon interactions at s=200 GeV, these measurements offer a unique opportunity to obtain information on the trigluon correlation functions. The measurements are performed at forward and backward rapidity (1.4
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(2017) Physical Review D. 95, 9, 092002. Abstract[All authors]
We report the first measurement of the fraction of J/ψ mesons coming from B-meson decay (FB→J/ψ) in p+p collisions at s=510 GeV. The measurement is performed using the forward silicon vertex detector and central vertex detector at PHENIX, which provide precise tracking and distance-of-closest-approach determinations, enabling the statistical separation of J/ψ due to B-meson decays from prompt J/ψ. The measured value of FB→J/ψ is 8.1%±2.3%(stat)±1.9%(syst) for J/ψ with transverse momenta 0
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(2017) Physical review D. 95, 9, 092003. Abstract
We report the first measurement of the full angular distribution for inclusive J/ψ→μ+μ- decays in p+p collisions at s=510 GeV. The measurements are made for J/ψ transverse momentum 2
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(2017) PHYSICAL REVIEW C. 95, 3, 034910. Abstract[All authors]
We present measurements of long-range angular correlations and the transverse momentum dependence of elliptic flow v2 in high-multiplicity p+Au collisions at sNN=200 GeV. A comparison of these results to previous measurements in high-multiplicity d+Au and He3+Au collisions demonstrates a relation between v2 and the initial collision eccentricity 2, suggesting that the observed momentum-space azimuthal anisotropies in these small systems have a collective origin and reflect the initial geometry. Good agreement is observed between the measured v2 and hydrodynamic calculations for all systems, and an argument disfavoring theoretical explanations based on initial momentum-space domain correlations is presented. The set of measurements presented here allows us to leverage the distinct intrinsic geometry of each of these systems to distinguish between different theoretical descriptions of the long-range correlations observed in small collision systems.
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(2017) PHYSICAL REVIEW C. 95, 3, 034904. Abstract[All authors]
The PHENIX Collaboration has measured the ratio of the yields of ψ(2S) to ψ(1S) mesons produced in p+p, p+Al, p+Au, and He3+Au collisions at sNN=200 GeV over the forward and backward rapidity intervals 1.2
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(2017) The European Physical Journal C (EPJ C). 77, 2, 70. Abstract[All authors]
Direct searches for lepton flavour violation in decays of the Higgs and Z bosons with the ATLAS detector at the LHC are presented. The following three decays are considered: H→ eτ, H→μτ, and Z→μτ. The searches are based on the data sample of protonproton collisions collected by the ATLAS detector corresponding to an integrated luminosity of 20.3fb-1 at a centre-of-mass energy of √s=8 TeV. No significant excess is observed, and upper limits on the lepton-flavour-violating branching ratios are set at the 95% confidence level: Br (H→ eτ)
2016
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(2016) Physical Review D. 94, 11, 112008. Abstract[All authors]
We report the double-helicity asymmetry, ALLJ/ψ, in inclusive J/ψ production at forward rapidity as a function of transverse momentum pT and rapidity |y|. The data analyzed were taken during s=510 GeV longitudinally polarized p+p collisions at the Relativistic Heavy Ion Collider in the 2013 run using the PHENIX detector. At this collision energy, J/ψ particles are predominantly produced through gluon-gluon scatterings, thus ALLJ/ψ is sensitive to the gluon polarization inside the proton. We measured ALLJ/ψ by detecting the decay daughter muon pairs μ+μ- within the PHENIX muon spectrometers in the rapidity range 1.2
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(2016) Nuclear Physics A. 956, p. 521-524 Abstract
The ATLAS experiment measures the production of muons coming from the decays of heavy flavour particles in the kinematic interval 4
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(2016) PHYSICAL REVIEW C. 94, 5, 054910. Abstract[All authors]
Measurements of anisotropic flow Fourier coefficients (vn) for inclusive charged particles and identified hadrons π±, K±, p, and p produced at midrapidity in Cu+Au collisions at sNN=200 GeV are presented. The data were collected in 2012 by the PHENIX experiment at the Relativistic Heavy-Ion Collider (RHIC). The particle azimuthal distributions with respect to different-order symmetry planes Ψn, for n=1, 2, and 3 are studied as a function of transverse momentum pT over a broad range of collision centralities. Mass ordering, as expected from hydrodynamic flow, is observed for all three harmonics. The charged-particle results are compared with hydrodynamical and transport model calculations. We also compare these Cu+Au results with those in Cu+Cu and Au+Au collisions at the same sNN and find that the v2 and v3, as a function of transverse momentum, follow a common scaling with 1/(nNpart1/3).
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(2016) Physical Review D. 93, 5, 052002. Abstract[All authors]
The ATLAS experiment has performed extensive searches for the electroweak production of charginos, neutralinos, and staus. This article summarizes and extends the search for electroweak supersymmetry with new analyses targeting scenarios not covered by previously published searches. New searches use vector-boson fusion production, initial-state radiation jets, and low-momentum lepton final states, as well as multivariate analysis techniques to improve the sensitivity to scenarios with small mass splittings and low-production cross sections. Results are based on 20 fb-1 of proton-proton collision data at √s = 8 TeV recorded with the ATLAS experiment at the Large Hadron Collider. No significant excess beyond Standard Model expectations is observed. The new and existing searches are combined and interpreted in terms of 95% confidence-level exclusion limits in simplified models, where a single production process and decay mode is assumed, as well as within phenomenological supersymmetric models.
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(2016) PHYSICAL REVIEW C. 93, 3, 034904. Abstract[All authors]
The PHENIX Collaboration at the Relativistic Heavy Ion Collider has measured open heavy flavor production in minimum bias Au+Au collisions at sNN=200 GeV via the yields of electrons from semileptonic decays of charm and bottom hadrons. Previous heavy flavor electron measurements indicated substantial modification in the momentum distribution of the parent heavy quarks owing to the quark-gluon plasma created in these collisions. For the first time, using the PHENIX silicon vertex detector to measure precision displaced tracking, the relative contributions from charm and bottom hadrons to these electrons as a function of transverse momentum are measured in Au+Au collisions. We compare the fraction of electrons from bottom hadrons to previously published results extracted from electron-hadron correlations in p+p collisions at sNN=200 GeV and find the fractions to be similar within the large uncertainties on both measurements for pT>4GeV/c. We use the bottom electron fractions in Au+Au and p+p along with the previously measured heavy flavor electron RAA to calculate the RAA for electrons from charm and bottom hadron decays separately. We find that electrons from bottom hadron decays are less suppressed than those from charm for the region 3
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(2016) Physical review D. 93, 5, 051103. Abstract[All authors]
We present midrapidity measurements from the PHENIX experiment of large parity-violating single-spin asymmetries of high transverse momentum electrons and positrons from W±/Z decays, produced in longitudinally polarized p+p collisions at center of mass energies of s=500 and 510 GeV. These asymmetries allow direct access to the antiquark polarized parton distribution functions due to the parity-violating nature of the W-boson coupling to quarks and antiquarks. The results presented are based on data collected in 2011, 2012, and 2013 with an integrated luminosity of 240 pb-1, which exceeds previous PHENIX published results by a factor of more than 27. These high Q2 data probe the parton structure of the proton at W mass scale and provide an important addition to our understanding of the antiquark parton helicity distribution functions at an intermediate Bjorken x value of roughly MW/s=0.16.
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(2016) Physical review letters. 116, 12, 122301. Abstract[All authors]
Jet production rates are measured in p+p and d+Au collisions at sNN=200 GeV recorded in 2008 with the PHENIX detector at the Relativistic Heavy Ion Collider. Jets are reconstructed using the R=0.3 anti-kt algorithm from energy deposits in the electromagnetic calorimeter and charged tracks in multiwire proportional chambers, and the jet transverse momentum (pT) spectra are corrected for the detector response. Spectra are reported for jets with 12
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(2016) PHYSICAL REVIEW C. 93, 2, 024904. Abstract[All authors]
The PHENIX experiment at the Relativistic Heavy Ion Collider has measured φ meson production and its nuclear modification in asymmetric Cu+Au heavy-ion collisions at sNN=200 GeV at both forward Cu-going direction (1.2
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(2016) PHYSICAL REVIEW C. 93, 2, 024901. Abstract[All authors]
Measurements of midrapidity charged-particle multiplicity distributions, dNch/dη, and midrapidity transverse-energy distributions, dET/dη, are presented for a variety of collision systems and energies. Included are distributions for Au+Au collisions at sNN=200, 130, 62.4, 39, 27, 19.6, 14.5, and 7.7 GeV, Cu+Cu collisions at sNN=200 and 62.4 GeV, Cu+Au collisions at sNN=200 GeV, U+U collisions at sNN=193 GeV, d+Au collisions at sNN=200 GeV, He3+Au collisions at sNN=200 GeV, and p+p collisions at sNN=200 GeV. Centrality-dependent distributions at midrapidity are presented in terms of the number of nucleon participants, Npart, and the number of constituent quark participants, Nqp. For all A+A collisions down to sNN=7.7 GeV, it is observed that the midrapidity data are better described by scaling with Nqp than scaling with Npart. Also presented are estimates of the Bjorken energy density, BJ, and the ratio of dET/dη to dNch/dη, the latter of which is seen to be constant as a function of centrality for all systems.
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(2016) PHYSICAL REVIEW C. 93, 2, 024911. Abstract[All authors]
Measurements of the fractional momentum loss (Sloss≡δpT/pT) of high-transverse-momentum-identified hadrons in heavy-ion collisions are presented. Using π0 in Au+Au and Cu+Cu collisions at sNN=62.4 and 200 GeV measured by the PHENIX experiment at the Relativistic Heavy Ion Collider and and charged hadrons in Pb+Pb collisions measured by the ALICE experiment at the Large Hadron Collider, we studied the scaling properties of Sloss as a function of a number of variables: the number of participants, Npart, the number of quark participants, Nqp, the charged-particle density, dNch/dη, and the Bjorken energy density times the equilibration time, Bjτ0. We find that the pT, where Sloss has its maximum, varies both with centrality and collision energy. Above the maximum, Sloss tends to follow a power-law function with all four scaling variables. The data at sNN=200 GeV and 2.76 TeV, for sufficiently high particle densities, have a common scaling of Sloss with dNch/dη and Bjτ0, lending insight into the physics of parton energy loss.
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(2016) Physical Review C. 93, 1, 011901. Abstract[All authors]
We report the measurement of cumulants (Cn,n=1,⋯,4) of the net-charge distributions measured within pseudorapidity (|η|
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(2016) Physical Review C. 93, 1, 014904. Abstract
We present measurements of e+e- production at midrapidity in Au+Au collisions at sNN=200 GeV. The invariant yield is studied within the PHENIX detector acceptance over a wide range of mass (mee
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(2016) Physical Review D. 93, 1, 011501. Abstract[All authors]
PHENIX measurements are presented for the cross section and double-helicity asymmetry (ALL) in inclusive π0 production at midrapidity from p+p collisions at s=510 GeV from data taken in 2012 and 2013 at the Relativistic Heavy Ion Collider. The next-to-leading-order perturbative-quantum-chromodynamics theory calculation is in excellent agreement with the presented cross section results. The calculation utilized parton-to-pion fragmentation functions from the recent DSS14 global analysis, which prefer a smaller gluon-to-pion fragmentation function. The π0ALL results follow an increasingly positive asymmetry trend with pT and s with respect to the predictions and are in excellent agreement with the latest global analysis results. This analysis incorporated earlier results on π0 and jet ALL and suggested a positive contribution of gluon polarization to the spin of the proton ΔG for the gluon momentum fraction range x>0.05. The data presented here extend to a currently unexplored region, down to x∼0.01, and thus provide additional constraints on the value of ΔG.
2015
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(2015) Physical Review C. 92, 4, 044909. Abstract[All authors]
The PHENIX Collaboration has measured φ meson production in d+Au collisions at sNN=200 GeV using the dimuon and dielectron decay channels. The φ meson is measured in the forward (backward) d-going (Au-going) direction, 1.2y2.2 (-2.2y-1.2) in the transverse-momentum (pT) range from 1-7 GeV/c and at midrapidity y0.35 in the pT range below 7 GeV/c. The φ meson invariant yields and nuclear-modification factors as a function of pT, rapidity, and centrality are reported. An enhancement of φ meson production is observed in the Au-going direction, while suppression is seen in the d-going direction, and no modification is observed at midrapidity relative to the yield in p+p collisions scaled by the number of binary collisions. Similar behavior was previously observed for inclusive charged hadrons and open heavy flavor, indicating similar cold-nuclear-matter effects.
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Measurements of Elliptic and Triangular Flow in High-Multiplicity He 3 +Au Collisions at sNN =200GeV(2015) Physical review letters. 115, 14, 142301. Abstract[All authors]
We present the first measurement of elliptic (v2) and triangular (v3) flow in high-multiplicity He3+Au collisions at sNN=200GeV. Two-particle correlations, where the particles have a large separation in pseudorapidity, are compared in He3+Au and in p+p collisions and indicate that collective effects dominate the second and third Fourier components for the correlations observed in the He3+Au system. The collective behavior is quantified in terms of elliptic v2 and triangular v3 anisotropy coefficients measured with respect to their corresponding event planes. The v2 values are comparable to those previously measured in d+Au collisions at the same nucleon-nucleon center-of-mass energy. Comparisons with various theoretical predictions are made, including to models where the hot spots created by the impact of the three He3 nucleons on the Au nucleus expand hydrodynamically to generate the triangular flow. The agreement of these models with data may indicate the formation of low-viscosity quark-gluon plasma even in these small collision systems.
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(2015) Physical Review C. 92, 3, 034913. Abstract[All authors]
We have studied the dependence of azimuthal anisotropy v2 for inclusive and identified charged hadrons in Au+Au and Cu+Cu collisions on collision energy, species, and centrality. The values of v2 as a function of transverse momentum pT and centrality in Au+Au collisions at sNN=200 and 62.4 GeV are the same within uncertainties. However, in Cu+Cu collisions we observe a decrease in v2 values as the collision energy is reduced from 200 to 62.4 GeV. The decrease is larger in the more peripheral collisions. By examining both Au+Au and Cu+Cu collisions we find that v2 depends both on eccentricity and the number of participants, Npart. We observe that v2 divided by eccentricity () monotonically increases with Npart and scales as Npart1/3. The Cu+Cu data at 62.4 GeV falls below the other scaled v2 data. For identified hadrons, v2 divided by the number of constituent quarks nq is independent of hadron species as a function of transverse kinetic energy KET=mT-m between 0.1
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(2015) Physical Review C. 92, 3, 034914. Abstract[All authors]
We present a systematic study of charged-pion and kaon interferometry in Au+Au collisions at sNN=200 GeV. The kaon mean source radii are found to be larger than pion radii in the outward and longitudinal directions for the same transverse mass; this difference increases for more central collisions. The azimuthal-angle dependence of the radii was measured with respect to the second-order event plane and similar oscillations of the source radii were found for pions and kaons. Hydrodynamic models qualitatively describe the similar oscillations of the mean source radii for pions and kaons, but they do not fully describe the transverse-mass dependence of the oscillations.
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(2015) Physical Review D. 91, 3, 032001. Abstract[All authors]
We present midrapidity charged-pion invariant cross sections, the ratio of the π- to π+ cross sections and the charge-separated double-spin asymmetries in polarized p + p collisions at p√s = 200 GeV. While the cross section measurements are consistent within the errors of next-to-leading-order (NLO) perturbative quantum chromodynamics predictions (pQCD), the same calculations overestimate the ratio of the charged-pion cross sections. This discrepancy arises from the cancellation of the substantial systematic errors associated with the NLO-pQCD predictions in the ratio and highlights the constraints these data will place on flavor-dependent pion fragmentation functions. The charge-separated pion asymmetries presented here sample an x range of ~0.03-0.16 and provide unique information on the sign of the gluon-helicity distribution.
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(2015) Physical Review C. 91, 2, 024913. Abstract[All authors]
Measurements of bottomonium production in heavy-ion and p+p collisions at the Relativistic Heavy Ion Collider (RHIC) are presented. The inclusive yield of the three Υ states, Υ(1S+2S+3S), was measured in the PHENIX experiment via electron-positron decay pairs at midrapidity for Au+Au and p+p collisions at sNN=200 GeV. The Υ(1S+2S+3S)→e+e- differential cross section at midrapidity was found to be Beedσ/dy=108±38(stat)±15(syst)±11(luminosity) pb in p+p collisions. The nuclear modification factor in the 30% most central Au+Au collisions indicates a suppression of the total Υ state yield relative to the extrapolation from p+p collision data. The suppression is consistent with measurements made by STAR at RHIC and at higher energies by the CMS experiment at the Large Hadron Collider.
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(2015) European Physical Journal C. 75, 1, 17. Abstract[All authors]
The jet energy scale (JES) and its systematic uncertainty are determined for jets measured with the ATLAS detector using protonproton collision data with a centre-ofmass energy of √s = 7 TeV corresponding to an integrated luminosity of 4.7 fb−1. Jets are reconstructed from energy deposits forming topological clusters of calorimeter cells using the anti-kt algorithm with distance parameters R = 0.4 or R = 0.6, and are calibrated using MC simulations. A residual JES correction is applied to account for differences between data and MC simulations. This correction and its systematic uncertainty are estimated using a combination of in situ techniques exploiting the transverse momentum balance between a jet and a For central jets at lower pT a Z boson, for 20 ≤ pjetTjetTT, the uncertainty is about 3 %. A consistent JES estimate is found using measurements of the calorimeter response of single hadrons in protonproton collisions and test-beam data, which also provide the estimate for pjetT > 1 TeV. The calibration of forward jets is derived from dijet pT balance measurements. The resulting uncertainty reaches its largest value of 6 % for low-pT jets at |η| =4.5. Additional JES uncertainties due to specific event topologies, such as close-by jets or selections of event samples with an enhanced content of jets originating from light quarks or gluons, are also discussed. The magnitude of these uncertainties depends on the event sample used in a given physics analysis, but typically amounts to 0.53 %.
2014
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(2014) Nuclear Instruments & Methods In Physics Research Section A-Accelerators Spectrometers Detectors And Associated Equipment. 768, p. 170-178 Abstract
The nucleus-nucleus impact parameter and collision geometry of a heavy ion collision are typically characterized by assigning a collision "centrality". In all present heavy ion experiments centrality is measured indirectly, by detecting the number of particles or the energy of the particles produced in the interactions, typically at high rapidity. Centrality parameters are associated to the measured detector response using the Glauber model. This approach suffers from systematic uncertainties related to the assumptions about the particle production mechanism and limitations of the Glauber model. In the collider based experiments there is a unique possibility to measure centrality parameters by registering spectator fragments remaining from the collision. This approach does not require model assumptions and relies on the fact that spectators and participants are related via the total number of nucleons in the colliding species. This paper describes the concept of a centrality detector for heavy ion experiment, which measures the total mass number of all fragments by measuring their deflection in the magnetic field of the collider elements.
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(2014) Nuclear Physics A. 932, p. 357-364 Abstract
The ATLAS experiment at the LHC has measured the centrality dependence of charged-particle pseudorapidity distribution, charged-particle spectra, and two-particle correlations in p+Pb collisions at a nucleon-nucleon centre-of-mass energy of sNN=5.02 TeV. Charged particles were measured over |η|
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(2014) Physical Review C. 90, 6, 064908. Abstract
We report on J/ψ production from asymmetric Cu+Au heavy-ion collisions at sNN=200 GeV at the Relativistic Heavy Ion Collider at both forward (Cu-going direction) and backward (Au-going direction) rapidities. The nuclear modification of J/ψ yields in Cu+Au collisions in the Au-going direction is found to be comparable to that in Au+Au collisions when plotted as a function of the number of participating nucleons. In the Cu-going direction, J/ψ production shows a stronger suppression. This difference is comparable in magnitude and has the same sign as the difference expected from shadowing effects due to stronger low-x gluon suppression in the larger Au nucleus.
[All authors] -
(2014) New Journal of Physics. 16, 113013. Abstract[All authors]
This paper presents a measurement of the cross-section for high transverse momentum W and Z bosons produced in pp collisions and decaying to all-hadronic final states. The data used in the analysis were recorded by the ATLAS detector at the CERN Large Hadron Collider at a centre-of-mass energy of and correspond to an integrated luminosity of . The measurement is performed by reconstructing the boosted W or Z bosons in single jets. The reconstructed jet mass is used to identify the W and Z bosons, and a jet substructure method based on energy cluster information in the jet centre-of-mass frame is used to suppress the large multi-jet background. The cross-section for events with a hadronically decaying W or Z boson, with transverse momentum and pseudorapidity , is measured to be pb and is compared to next-to-leading-order calculations. The selected events are further used to study jet grooming techniques.
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(2014) Journal of High Energy Physics. 2014, 10, 96. Abstract[All authors]
Results of a search for the electroweak associated production of charginos and next-to-lightest neutralinos, pairs of charginos or pairs of tau sleptons are presented. These processes are characterised by final states with at least two hadronically decaying tau leptons, missing transverse momentum and low jet activity. The analysis is based on an integrated luminosity of 20.3 fb-1 of proton-proton collisions at√s = 8 TeV recorded with the ATLAS experiment at the Large Hadron Collider. No significant excess is observed with respect to the predictions from Standard Model processes. Limits are set at 95% confidence level on the masses of the lighter chargino and next-to-lightest neutralino for various hypotheses for the lightest neutralino mass in simplified models. In the scenario of direct production of chargino pairs, with each chargino decaying into the lightest neutralino via an intermediate tau slepton, chargino masses up to 345 GeV are excluded for a massless lightest neutralino. For associated production of mass-degenerate charginos and next-to-lightest neutralinos, both decaying into the lightest neutralino via an intermediate tau slepton, masses up to 410 GeV are excluded for a massless lightest neutralino.
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(2014) Physical Review C. 90, 3, 034902. Abstract[All authors]
High-energy proton- and deuteron-nucleus collisions provide an excellent tool for studying a wide array of physics effects, including modifications of parton distribution functions in nuclei, gluon saturation, and color neutralization and hadronization in a nuclear environment, among others. All of these effects are expected to have a significant dependence on the size of the nuclear target and the impact parameter of the collision, also known as the collision centrality. In this article, we detail a method for determining centrality classes in p(d)+A collisions via cuts on the multiplicity at backward rapidity (i.e., the nucleus-going direction) and for determining systematic uncertainties in this procedure. For d+Au collisions at sNN=200 GeV we find that the connection to geometry is confirmed by measuring the fraction of events in which a neutron from the deuteron does not interact with the nucleus. As an application, we consider the nuclear modification factors Rp(d)+A, for which there is a bias in the measured centrality-dependent yields owing to auto correlations between the process of interest and the backward-rapidity multiplicity. We determine the bias-correction factors within this framework. This method is further tested using the hijing Monte Carlo generator. We find that for d+Au collisions at sNN=200 GeV, these bias corrections are small and vary by less than 5% (10%) up to pT=10 (20) GeV/c. In contrast, for p+Pb collisions at sNN=5.02 TeV we find that these bias factors are an order of magnitude larger and strongly pT dependent, likely attributable to the larger effect of multiparton interactions.
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(2014) Physical Review D. 90, 5, 052002. Abstract[All authors]
The PHENIX experiment at the Relativistic Heavy Ion Collider has measured low-mass vector-meson, ω, ρ, and φ, production through the dimuon decay channel at forward rapidity (1.2
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System-size dependence of open-heavy-flavor production in nucleus-nucleus collisions at sNN =200 GeV(2014) Physical Review C. 90, 3, 034903. Abstract[All authors]
The PHENIX Collaboration at the Relativistic Heavy Ion Collider has measured open-heavy-flavor production in Cu+Cu collisions at sNN=200 GeV through the measurement of electrons at midrapidity that originate from semileptonic decays of charm and bottom hadrons. In peripheral Cu+Cu collisions an enhanced production of electrons is observed relative to p+p collisions scaled by the number of binary collisions. In the transverse momentum range from 1 to 5 GeV/c the nuclear modification factor is RAA∼1.4. As the system size increases to more central Cu+Cu collisions, the enhancement gradually disappears and turns into a suppression. For pT>3 GeV/c, the suppression reaches RAA∼0.8 in the most central collisions. The pT and centrality dependence of RAA in Cu+Cu collisions agree quantitatively with RAA in d+Au and Au+Au collisions, if compared at a similar number of participating nucleons.
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(2014) Physical Review D. 90, 1, 012006. Abstract[All authors]
Measurements of transverse-single-spin asymmetries (AN) in p+p collisions at s=62.4 and 200 GeV with the PHENIX detector at the Relativistic Heavy Ion Collider are presented. At midrapidity, AN is measured for neutral pion and eta mesons reconstructed from diphoton decay, and, at forward rapidities, neutral pions are measured using both diphotons and electromagnetic clusters. The neutral-pion measurement of AN at midrapidity is consistent with zero with uncertainties a factor of 20 smaller than previous publications, which will lead to improved constraints on the gluon Sivers function. At higher rapidities, where the valence quark distributions are probed, the data exhibit sizable asymmetries. In comparison with previous measurements in this kinematic region, the new data extend the kinematic coverage in s and pT, and it is found that the asymmetries depend only weakly on s. The origin of the forward AN is presently not understood quantitatively. The extended reach to higher pT probes the transition between transverse momentum dependent effects at low pT and multiparton dynamics at high pT.
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(2014) Physical Review D. 90, 1, 012007. Abstract[All authors]
Results are presented from data recorded in 2009 by the PHENIX experiment at the Relativistic Heavy Ion Collider for the double-longitudinal spin asymmetry, ALL, for π0 and η production in s=200GeV polarized p+p collisions. Comparison of the π0 results with different theory expectations based on fits of other published data showed a preference for small positive values of gluon polarization, ΔG, in the proton in the probed Bjorken x range. The effect of adding the new 2009 π0 data to a recent global analysis of polarized scattering data is also shown, resulting in a best fit value ΔGDSSV[0.05,0.2]=0.06-0.15+0.11 in the range 0.05
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(2014) Physical review letters. 112, 25, 252301. Abstract[All authors]
The PHENIX experiment has measured open heavy-flavor production via semileptonic decay over the transverse momentum range 1
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(2014) Physical Review C. 89, 4, 044905. Abstract[All authors]
Measurements of the midrapidity transverse-energy distribution, dET/dη, are presented for p+p, d+Au, and Au+Au collisions at sNN=200 GeV and additionally for Au+Au collisions at sNN=62.4 and 130 GeV. The dET/dη distributions are first compared with the number of nucleon participants Npart, number of binary collisions Ncoll, and number of constituent-quark participants Nqp calculated from a Glauber model based on the nuclear geometry. For Au+Au, dET/d/Npart increases with Npart, while dET/d/Nqp is approximately constant for all three energies. This indicates that the two-component ansatz, dET/d (1-x)Npart/2+xNcoll, which was used to represent ET distributions, is simply a proxy for Nqp, and that the Ncoll term does not represent a hard-scattering component in ET distributions. The dET/dη distributions of Au+Au and d+Au are then calculated from the measured p+p ET distribution using two models that both reproduce the Au+Au data. However, while the number-of-constituent-quark- participant model agrees well with the d+Au data, the additive-quark model does not.
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(2014) Physical Review C. 89, 3, 034915. Abstract[All authors]
Background: Heavy-flavor modification in relativistic p(d)+A collisions are sensitive to different kinds of strong-interaction physics ranging from modifications of the nuclear wave function to initial- and final-state energy loss. Modifications to single heavy-flavor particles and their decay leptons at midrapidity and forward rapidity are well established at the Relativistic Heavy Ion Collider (RHIC). Purpose: This paper presents measurements of azimuthal correlations of electron-muon pairs produced from heavy-flavor decays, primarily cc̄, in sNN=200 GeV p+p and d+Au collision using the PHENIX detector at RHIC. The electrons are measured at midrapidity while the muons in the pair are measured at forward rapidity, defined as the direction of the deuteron beam, in order to utilize the deuteron to probe low-x partons in the gold nucleus. Methods: This analysis uses the central spectrometer arms for electron identification and forward spectrometer arms for muon identification. Azimuthal correlations are built in all sign combinations for e-μ pairs. Subtracting the like-sign yield from the unlike-sign yield removes the correlations from light flavor decays and conversions. Results: Comparing the p+p results with several different Monte Carlo event generators, we find the results are consistent with a total charm cross section σcc̄=538±46 (stat) ± 197 (data syst) ± 174 (model syst) μb. These generators also indicate that the back-to-back peak at Δφ=π is dominantly from the leading-order contributions (gluon fusion), while higher-order processes (flavor excitation and gluon splitting) contribute to the yield at all Δφ. We observe a suppression in the pair yield per collision in d+Au. We find the pair yield suppression factor for 2.7
2013
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(2013) Physical Review C. 88, 6, 064910. Abstract[All authors]
The azimuthal anisotropy coefficients v2 and v4 of π0 and η mesons are measured in Au + Au collisions at sNN=200 GeV as a function of transverse momentum pT (1-14 GeV/c) and centrality. The extracted v2 coefficients are found to be consistent between the two meson species over the measured pT range. The ratio of v4/v22 for π0 mesons is found to be independent of pT for 1-9 GeV/c, implying a lack of sensitivity of the ratio to the change of underlying physics with pT. Furthermore, the ratio of v4/v22 is systematically larger in central collisions, which may reflect the combined effects of fluctuations in the initial collision geometry and finite viscosity in the evolving medium.
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(2013) Physical review letters. 111, 20, 202301. Abstract[All authors]
We present results for three charmonia states (ψ, χc, and J/ψ) in d+Au collisions at |y|
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(2013) Physical review letters. 111, 21, 212301. Abstract[All authors]
The PHENIX collaboration at the Relativistic Heavy Ion Collider (RHIC) reports measurements of azimuthal dihadron correlations near midrapidity in d+Au collisions at √sNN=200 GeV. These measurements complement recent analyses by experiments at the Large Hadron Collider (LHC) involving central p+Pb collisions at √sNN=5.02 TeV, which have indicated strong anisotropic long-range correlations in angular distributions of hadron pairs. The origin of these anisotropies is currently unknown. Various competing explanations include parton saturation and hydrodynamic flow. We observe qualitatively similar, but larger, anisotropies in d+Au collisions at RHIC compared to those seen in p+Pb collisions at the LHC. The larger extracted v2 values in d+Au are consistent with expectations from hydrodynamic calculations owing to the larger expected initial-state eccentricity compared with that from p+Pb collisions. When both are divided by an estimate of the initial-state eccentricity the scaled anisotropies follow a common trend with multiplicity that may extend to heavy ion data at RHIC and the LHC, where the anisotropies are widely thought to arise from hydrodynamic flow.
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(2013) Physical Review C. 88, 2, 024906. Abstract[All authors]
The transverse momentum (pT) spectra and ratios of identified charged hadrons (π±, K±, p, p̄) produced in √sNN=200 GeV Au+Au and d+Au collisions are reported in five different centrality classes for each collision species. The measurements of pions and protons are reported up to pT=6 GeV/c (5 GeV/c), and the measurements of kaons are reported up to pT=4 GeV/c (3.5 GeV/c) in Au+Au (d+Au) collisions. In the intermediate pT region, between 2 and 5 GeV/c, a significant enhancement of baryon-to-meson ratios compared to those measured in p+p collisions is observed. This enhancement is present in both Au+Au and d+Au collisions and increases as the collisions become more central. We compare a class of peripheral Au+Au collisions with a class of central d+Au collisions which have a comparable number of participating nucleons and binary nucleon-nucleon collisions. The pT-dependent particle ratios for these classes display a remarkable similarity, which is then discussed.
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(2013) Physical review letters. 111, 3, 032301. Abstract[All authors]
The jet fragmentation function is measured with direct photon-hadron correlations in p+p and Au+Au collisions at √sNN=200 GeV. The pT of the photon is an excellent approximation to the initial p T of the jet and the ratio zT=pTh/pTγ is used as a proxy for the jet fragmentation function. A statistical subtraction is used to extract the direct photon-hadron yields in Au+Au collisions while a photon isolation cut is applied in p+p. IAA, the ratio of hadron yield opposite the photon in Au+Au to that in p+p, indicates modification of the jet fragmentation function. Suppression, most likely due to energy loss in the medium, is seen at high zT. The associated hadron yield at low z T is enhanced at large angles. Such a trend is expected from redistribution of the lost energy into increased production of low-momentum particles.
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(2013) Physical Review C. 87, 5, 054907. Abstract[All authors]
Direct photons have been measured in √sNN=200 GeV d+Au collisions at midrapidity. A wide pT range is covered by measurements of nearly real virtual photons (1
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(2013) Nuclear Physics A. 904-905, p. 326c-333c Abstract
A broad range of new experimental data and theoretical results on the properties of hadronic matter under extreme conditions have been reported at Quark Matter 2012 conference. At this conference the scientific community was presented with a variety of measurements from the 2011 lead-lead LHC run using hard probe observables. Many measurements, such as boson-jet correlations, production rates of the b-jets, high precision jet fragmentation and others were shown for the first time. The new data from the LHC was matched by new techniques and analyses coming from RHIC experiments. This proceedings article summarises the new measurements with high-p T particles and jets and attempts to provide a theoretical explanation for the novel results presented at the conference.
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(2013) Proceedings of Science. Abstract[All authors]
We present a panel discussion about our current state of knowledge about the Quark-Gluon Plasma. The nine panelists were asked to address the question: What do we want to know about the quark-gluon plasma, and how can we find the answers? The contributions illuminate our present understanding and highlight various aspects of the ongoing debate about the future directions of relativistic heavy-ion collision research.
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(2013) Physical Review C. 87, 4, 044909. Abstract[All authors]
The three Υ states, Υ(1S+2S+3S), are measured in d+Au and p+p collisions at √sNN=200 GeV and rapidities 1.2
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(2013) Physical Review C. 87, 3, 034904. Abstract[All authors]
We present measured J/ψ production rates in d+Au collisions at √sNN=200 GeV over broad ranges of transverse momentum (pT=0-14 GeV/c) and rapidity (-2.2
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(2013) Physics Letters B. 720, 4-5, p. 277-308 Abstract[All authors]
A search for long-lived particles is performed using a data sample of 4.7 fb-1 from proton-proton collisions at a centre-of-mass energy. √s = 7 TeV collected by the ATLAS detector at the LHC. No excess is observed above the estimated background and lower limits, at 95% confidence level, are set on the mass of the long-lived particles in different scenarios, based on their possible interactions in the inner detector, the calorimeters and the muon spectrometer. Long-lived staus in gauge-mediated SUSY-breaking models are excluded up to a mass of 300 GeV for tan β = 5-20. Directly produced long-lived sleptons are excluded up to a mass of 278 GeV. R-hadrons, composites of gluino (stop, sbottom) and light quarks, are excluded up to a mass of 985 GeV (683 GeV, 612 GeV) when using a generic interaction model. Additionally two sets of limits on R-hadrons are obtained that are less sensitive to the interaction model for R-hadrons. One set of limits is obtained using only the inner detector and calorimeter observables, and a second set of limits is obtained based on the inner detector alone. (c) 2013 CERN. Published by Elsevier B.V. All rights reserved.
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(2013) Physical Review C. 87, 3, 034911. Abstract[All authors]
The PHENIX experiment has measured the production of π0s in Au+Au collisions at √sNN = 200 GeV. The new data offer a fourfold increase in recorded luminosity, providing higher precision and a larger reach in transverse momentum, pT, to 20 GeV/c. The production ratio of η/π0 is 0.46±0.01(stat)±0.05(syst), constant with p T and collision centrality. The observed ratio is consistent with earlier measurements, as well as with the p+p and d+Au values. π0 are suppressed by a factor of 5, as in earlier findings. However, with the improved statistical precision a small but significant rise of the nuclear modification factor RAA vs pT, with a slope of 0.0106±0.00290. 0034 (Gev/c)-1, is discernible in central collisions. A phenomenological extraction of the average fractional parton energy loss shows a decrease with increasing pT. To study the path-length dependence of suppression, the π0 yield is measured at different angles with respect to the event plane; a strong azimuthal dependence of the π0 RAA is observed. The data are compared to theoretical models of parton energy loss as a function of the path length L in the medium. Models based on perturbative quantum chromodynamics are insufficient to describe the data, while a hybrid model utilizing pQCD for the hard interactions and anti-de-Sitter space/conformal field theory (AdS/CFT) for the soft interactions is consistent with the data.
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(2013) Physical Review D. 87, 1, 012011. Abstract[All authors]
We report on the first measurement of the double-spin asymmetry, A LL, of electrons from the decays of hadrons containing heavy flavor in longitudinally polarized p+p collisions at √s=200 GeV for p T=0.5 to 3.0 GeV/c. The asymmetry was measured at midrapidity (|η|
2012
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(2012) Physical Review C. 86, 6, 064901. Abstract[All authors]
We present measurements of the J/ψ invariant yields in √s NN=39 and 62.4 GeV Au + Au collisions at forward rapidity (1.2
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(2012) Physical review letters. 109, 24, 242301. Abstract[All authors]
The PHENIX experiment has measured electrons and positrons at midrapidity from the decays of hadrons containing charm and bottom quarks produced in d+Au and p+p collisions at √sNN=200GeV in the transverse-momentum range 0.85≤pTe≤8.5GeV/c. In central d+Au collisions, the nuclear modification factor RdA at 1.5
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(2012) Physical Review D - Particles, Fields, Gravitation and Cosmology. 86, 9, 099904. Abstract[All authors]
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(2012) Physical Review D. 86, 7, 072008. Abstract[All authors]
The differential cross section for the production of direct photons in p+p collisions at √s=200GeV at midrapidity was measured in the PHENIX detector at the Relativistic Heavy Ion Collider. Inclusive direct photons were measured in the transverse momentum range from 5.5-25GeV/c, extending the range beyond previous measurements. Event structure was studied with an isolation criterion. Next-to-leading-order perturbative-quantum-chromodynamics calculations give a good description of the spectrum. When the cross section is expressed versus x T, the PHENIX data are seen to be in agreement with measurements from other experiments at different center-of-mass energies.
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(2012) Physical review letters. 109, 15, 152302. Abstract[All authors]
We report the measurement of direct photons at midrapidity in Au+Au collisions at √s NN=200GeV. The direct photon signal was extracted for the transverse momentum range of 4GeV/c
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(2012) Physical review letters. 109, 15, 152301. Abstract[All authors]
Neutral-pion π0 spectra were measured at midrapidity (|y|
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(2012) Physical review letters. 109, 12, 122302. Abstract[All authors]
The second Fourier component v2 of the azimuthal anisotropy with respect to the reaction plane was measured for direct photons at midrapidity and transverse momentum (pT) of 1-13 GeV/c in Au+Au collisions at √SNN = 200 GeV. Previous measurements of this quantity for hadrons with pT 6 GeV/c a reduced anisotropy is interpreted in terms of a path-length dependence for parton energy loss. In this measurement with the PHENIX detector at the Relativistic Heavy Ion Collider we find that for pT > 4 GeV/c the anisotropy for direct photons is consistent with zero, as expected if the dominant source of direct photons is initial hard scattering. However, in the pT 2 comparable to that of hadrons, whereas model calculations for thermal photons in this kinematic region significantly underpredict the observed v2.
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(2012) Physical Review C. 86, 2, 024909. Abstract[All authors]
Background: Heavy-flavor production in p + p collisions is a good test of perturbative-quantum-chromodynamics (pQCD) calculations. Modification of heavy-flavor production in heavy-ion collisions relative to binary-collision scaling from p + p results, quantified with the nuclear-modification factor (RAA), provides information on both cold- and hot-nuclear-matter effects. Midrapidity heavy-flavor RAA measurements at the Relativistic Heavy Ion Collider have challenged parton-energy-loss models and resulted in upper limits on the viscosity-entropy ratio that are near the quantum lower bound. Such measurements have not been made in the forward-rapidity region. Purpose: Determine transverse-momentum (pT) spectra and the corresponding RAA for muons from heavy-flavor meson decay in p + p and Cu + Cu collisions at √sNN=200 GeV and y=1.65. Method: Results are obtained using the semileptonic decay of heavy-flavor mesons into negative muons. The PHENIX muon-arm spectrometers measure the pT spectra of inclusive muon candidates. Backgrounds, primarily due to light hadrons, are determined with a Monte Carlo calculation using a set of input hadron distributions tuned to match measured-hadron distributions in the same detector and statistically subtracted. Results: The charm-production cross section in p + p collisions at √s=200 GeV, integrated over pT and in the rapidity range 1.4
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(2012) Physical Review C. 85, 6, 064914. Abstract[All authors]
Measurements of the anisotropy parameter v2 of identified hadrons (pions, kaons, and protons) as a function of centrality, transverse momentum pT, and transverse kinetic energy KET at midrapidity (|η|
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(2012) Physical Review D. 85, 9, 092004. Abstract[All authors]
We report on charmonium measurements [J/ψ (1S), ψ (2S), and χ c (1P)] in p+p collisions at √s=200GeV. We find that the fraction of J/ψ coming from the feed-down decay of ψ and χ c in the midrapidity region (|y|
2011
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(2011) Journal Of Physics G-Nuclear And Particle Physics. 38, 12, 124135. Abstract
The PHENIX experiment was upgraded with the Hadron Blind Detector (HBD) for the measurement of low-mass electron pairs. The HBD reduces the combinatorial background by providing additional electron identification in a field-free region close to the vertex and by exploiting the small opening angle of the pi(0) Dalitz and conversion pairs. The HBD was successfully operated during Run 9 and Run 10 at the RHIC in the measurements of e(+)e(-) pairs in p+p and Au+Au collisions, respectively. This paper reports on the present status of the dielectron analysis in Au+Au collisions at root s(NN) = 200 GeV.
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(2011) Journal Of Physics G-Nuclear And Particle Physics. 38, 12, 124082. Abstract
The PHENIX experiment at the RHIC has measured various light mesons using multiple decay channels over a wide range of transverse momenta. In these proceedings, we present a review of the most recent results on the production of omega, phi, K*, K-s in p+p collisions and their nuclear modification factors in d+Au, Cu+Cu and Au+Au collisions at root s(NN) = 200 GeV. Results of phi production at root s(NN) = 62.4 GeV are also discussed.
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(2011) Physical review letters. 107, 25, 252301. Abstract[All authors]
Flow coefficients vn for n=2, 3, 4, characterizing the anisotropic collective flow in Au+Au collisions at √sNN=200GeV, are measured relative to event planes Ψn, determined at large rapidity. We report vn as a function of transverse momentum and collision centrality, and study the correlations among the event planes of different order n. The vn are well described by hydrodynamic models which employ a Glauber Monte Carlo initial state geometry with fluctuations, providing additional constraining power on the interplay between initial conditions and the effects of viscosity as the system evolves. This new constraint can serve to improve the precision of the extracted shear viscosity to entropy density ratio η/s.
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(2011) Physical Review C. 84, 5, 054912. Abstract[All authors]
Heavy quarkonia are observed to be suppressed in relativistic heavy-ion collisions relative to their production in p+p collisions scaled by the number of binary collisions. In order to determine if this suppression is related to color screening of these states in the produced medium, one needs to account for other nuclear modifications including those in cold nuclear matter. In this paper, we present new measurements from the PHENIX 2007 data set of J/ψ yields at forward rapidity (1.2
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(2011) Physical Review C. 84, 4, 044905. Abstract[All authors]
Transverse momentum spectra of electrons (pTe) from semileptonic weak decays of heavy-flavor mesons in the range of 0.3
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(2011) Physical review letters. 107, 14, 142301. Abstract[All authors]
We present measurements of J/ψ yields in d+Au collisions at √sNN=200GeV recorded by the PHENIX experiment and compare them with yields in p+p collisions at the same energy per nucleon-nucleon collision. The measurements cover a large kinematic range in J/ψ rapidity (-2.2
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(2011) Physics Letters B. 703, 4, p. 428-446 Abstract[All authors]
A search for long-lived charged particles reaching the muon spectrometer is performed using a data sample of 37 pb-1 from pp collisions at √s = 7 TeV collected by the ATLAS detector at the LHC in 2010. No excess is observed above the estimated background. Stable τ over bar sleptons are excluded at 95% CL up to a mass of 136 GeV, in GMSB models with N-5 = 3 ,mmessenger = 250 TeV, sign(μ) = 1 and tan β = 5. Electroweak production of sleptons is excluded up to a mass of 110 GeV. Gluino R-hadrons in a generic interaction model are excluded up to masses of 530 GeV to 544 GeV depending on the fraction of R-hadrons produced as (g) over bar -balls.
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(2011) Physical Review C. 84, 2, 024904. Abstract[All authors]
Pair correlations between large transverse momentum neutral pion triggers (pT=4 - 7 GeV/c) and charged hadron partners (pT=3 - 7 GeV/c) in central (0%-20%) and midcentral (20%-60%) Au+Au collisions at √sNN=200 GeV are presented as a function of trigger orientation with respect to the reaction plane. The particles are at larger momentum than where jet shape modifications have been observed, and the correlations are sensitive to the energy loss of partons traveling through hot dense matter. An out-of-plane trigger particle produces only 26±20% of the away-side pairs that are observed opposite of an in-plane trigger particle for midcentral (20%-60%) collisions. In contrast, near-side jet fragments are consistent with no suppression or dependence on trigger orientation with respect to the reaction plane. These observations are qualitatively consistent with a picture of little near-side parton energy loss either due to surface bias or fluctuations and increased away-side parton energy loss due to a long path through the medium. The away-side suppression as a function of reaction-plane angle is shown to be sensitive to both the energy loss mechanism and the space-time evolution of heavy-ion collisions.
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Design, construction, operation and performance of a Hadron Blind Detector for the PHENIX experiment(2011) Nuclear Instruments & Methods In Physics Research Section A-Accelerators Spectrometers Detectors And Associated Equipment. 646, 1, p. 35-58 Abstract[All authors]
A Hadron Blind Detector (HBD) has been developed, constructed and successfully operated within the PHENIX detector at RHIC. The HBD is a Cherenkov detector operated with pure CF4. It has a 50 cm long radiator directly coupled in a windowless configuration to a readout element consisting of a triple GEM stack, with a CsI photocathode evaporated on the top surface of the top GEM and pad readout at the bottom of the stack. This paper gives a comprehensive account of the construction, operation and in-beam performance of the detector.
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(2011) Nuclear Physics A. 862-63, p. 198-204 Abstract
These proceedings summarize the di-electron spectrum measurements by PHENIX in p + p and Au + Au collisions at root S-NN = 200 GeV, along with a comparison to the expectations from hadronic sources and various model predictions. An overview of the latest PHENIX results on open heavy flavor and quarkonia production. measured through the electron and (main channels at mid-rapidity and forward/backward rapidity for p + p, d + Au and Au + Au collisions is also presented.
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(2011) Physical Review D. 84, 1, 012006. Abstract[All authors]
We report on the event structure and double helicity asymmetry (A LL) of jet production in longitudinally polarized p+p collisions at √s=200GeV. Photons and charged particles were measured by the PHENIX experiment at midrapidity |η|2GeV/c) photon in the event. Event structure, such as multiplicity, pT density and thrust in the PHENIX acceptance, were measured and compared with the results from the pythia event generator and the geant detector simulation. The shape of jets and the underlying event were well reproduced at this collision energy. For the measurement of jet ALL, photons and charged particles were clustered with a seed-cone algorithm to obtain the cluster pT sum (pTreco). The effect of detector response and the underlying events on pTreco was evaluated with the simulation. The production rate of reconstructed jets is satisfactorily reproduced with the next-to-leading-order and perturbative quantum chromodynamics jet production cross section. For 4
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(2011) Physical Review C. 83, 6, 064903. Abstract[All authors]
Transverse momentum distributions and yields for π±, K±, p, and p in p+p collisions at √s = 200 and 62.4 GeV at midrapidity are measured by the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC). These data provide important baseline spectra for comparisons with identified particle spectra in heavy ion collisions at RHIC. We present the inverse slope parameter Tinv, mean transverse momentum pT, and yield per unit rapidity dN/dy at each energy, and compare them to other measurements at different √s in p+p and p+p collisions. We also present the scaling properties such as mT scaling and x T scaling on the pT spectra between different energies. To discuss the mechanism of the particle production in p+p collisions, the measured spectra are compared to next-to-leading-order or next-to-leading- logarithmic perturbative quantum chromodynamics calculations.
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(2011) Physical Review C. 83, 4, 044912. Abstract[All authors]
Measurements of electrons from the decay of open-heavy-flavor mesons have shown that the yields are suppressed in Au+Au collisions compared to expectations from binary-scaled p+p collisions. These measurements indicate that charm and bottom quarks interact with the hot dense matter produced in heavy-ion collisions much more than expected. Here we extend these studies to two-particle correlations where one particle is an electron from the decay of a heavy-flavor meson and the other is a charged hadron from either the decay of the heavy meson or from jet fragmentation. These measurements provide more detailed information about the interactions between heavy quarks and the matter, such as whether the modification of the away-side-jet shape seen in hadron-hadron correlations is present when the trigger particle is from heavy-meson decay and whether the overall level of away-side-jet suppression is consistent. We statistically subtract correlations of electrons arising from background sources from the inclusive electron-hadron correlations and obtain two-particle azimuthal correlations at √sNN=200 GeV between electrons from heavy-flavor decay with charged hadrons in p+p and also first results in Au+Au collisions. We find the away-side-jet shape and yield to be modified in Au+Au collisions compared to p+p collisions.
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(2011) Nuclear Physics A. 855, 1, p. 265-268 Abstract
The Hadron Blind Detector (HBD) was developed, installed and successfully operated in the PHENIX detector during RHIC Runs in 2009 (p+p) and 2010 (Au+Au). The HBD is a windowless Cherenkov detector, operated with CF4 gas in proximity focus configuration. It uses triple GEM elements for signal amplification with CsI photocathode evaporated on top of the first GEM. The purpose of the HBD is to reduce the combinatorial background from the dielectron invariant mass spectrum by recognizing and rejecting e(+) or e(-) originating from pi(0) Dalitz decays and conversion. This article reports on the in-beam performance of the HBD.
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(2011) Nuovo Cimento della Societa Italiana di Fisica C. 34, 2, p. 109-117 Abstract
This proceeding gives the most complete review of the measurements of the ø-meson production in relativistic heavy ion and proton-proton collisions performed by the PHENIX experiment at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. The measurements of the f-meson are consistent in the analysis of various decay modes, using different techniques. The results show expected similarities when analyzed in Au + Au and Cu + Cu collision systems for the corresponding centrality classes. In other systems PHENIX observes not only the difference between the suppression of f-meson and the proton, reflecting generally different behavior between mesons and baryons, but also a significant difference in suppression of different mesons. These results are hard to explain due to the mass or quark content of the f-meson. PACS 21.65.Jk-Mesons in nuclear matter. PACS 25.75.Dw-Particle and resonance production.
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(2011) Physical Review D. 83, 5, 052004. Abstract[All authors]
The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the invariant differential cross section for production of KS0, ω, η, and φ mesons in p+p collisions at √s=200GeV. Measurements of ω and φ production in different decay channels give consistent results. New results for the ω are in agreement with previously published data and extend the measured pT coverage. The spectral shapes of all hadron transverse momentum distributions measured by PHENIX are well described by a Tsallis distribution functional form with only two parameters, n and T, determining the high-pT and characterizing the low-pT regions of the spectra, respectively. The values of these parameters are very similar for all analyzed meson spectra, but with a lower parameter T extracted for protons. The integrated invariant cross sections calculated from the fitted distributions are found to be consistent with existing measurements and with statistical model predictions.
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(2011) Physical Review C. 83, 2, 024909. Abstract[All authors]
The PHENIX experiment at the Relativistic Heavy Ion Collider has performed systematic measurements of φ meson production in the K+K - decay channel at midrapidity in p+p, d+Au, Cu+Cu, and Au+Au collisions at √sNN=200GeV. Results are presented on the φ invariant yield and the nuclear modification factor RAA for Au+Au and Cu+Cu, and RdA for d+Au collisions, studied as a function of transverse momentum (1
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(2011) Physical Review D. 83, 3, 032001. Abstract[All authors]
Measurements of double-helicity asymmetries in inclusive hadron production in polarized p+p collisions are sensitive to helicity-dependent parton distribution functions, in particular, to the gluon helicity distribution, Δg. This study focuses on the extraction of the double-helicity asymmetry in η production (p→+p→→η+X), the η cross section, and the η/π0 cross section ratio. The cross section and ratio measurements provide essential input for the extraction of fragmentation functions that are needed to access the helicity-dependent parton distribution functions.
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(2011) Journal Of Physics G-Nuclear And Particle Physics. 38, 2, 25002. Abstract
Based on the statistical hadronizationmodel, we obtain quantitative predictions for the relative abundances of hadron species in pp collisions at the LHC. By using the parameters of the model determined at √s = 200 GeV, and extrapolating the overall normalization from pp̄ collisions at the SPS and Tevatron, we find that the expected rapidity densities are almost grandcanonical. Therefore, at LHC the ratios between different species become essentially energy-independent, provided that the hadronization temperature TH and the strangeness suppression factor γS retain the stable values observed in the presently explored range of pp and pp̄ collisions.
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(2011) Physical review letters. 106, 6, 062001. Abstract[All authors]
Large parity-violating longitudinal single-spin asymmetries ALe +=-0.86-0.14+0.30 and ALe-=0.88-0.71+0.12 are observed for inclusive high transverse momentum electrons and positrons in polarized p+p collisions at a center-of-mass energy of √s=500GeV with the PHENIX detector at RHIC. These e± come mainly from the decay of W± and Z0 bosons, and their asymmetries directly demonstrate parity violation in the couplings of the W± to the light quarks. The observed electron and positron yields were used to estimate W ± boson production cross sections for the e± channels of σ(pp→W+X)×BR(W+→e +νe)=144.1±21.2(stat)-10.3+3.4(syst)±21. 6(norm)pb, and σ(pp→W-X)×BR(W -→e-ν̄e)=31.7±12.1(stat)-8. 2+10.1(syst)±4.8(norm)pb.
2010
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(2010) Physical Review D. 82, 11, 112008. Abstract[All authors]
We report the first measurement of transverse single-spin asymmetries in J/ψ production from transversely polarized p+p collisions at √s=200GeV with data taken by the PHENIX experiment in 2006 and 2008. The measurement was performed over the rapidity ranges 1.2
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(2010) Physical review letters. 105, 14, 142301. Abstract[All authors]
We have measured the azimuthal anisotropy of π0 production for 1
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(2010) Physical Review C. 82, 1, 011902. Abstract[All authors]
New measurements by the PHENIX experiment at the Relativistic Heavy Ion Collider for η production at midrapidity as a function of transverse momentum (pT) and collision centrality in √sNN=200 GeV Au+Au and p+p collisions are presented. They indicate nuclear modification factors (RAA) which are similar in both magnitude and trend to those found in earlier π0 measurements. Linear fits to RAA as a function of pT in 5-20 GeV/c show that the slope is consistent with zero within two standard deviations at all centralities, although a slow rise cannot be excluded. Having different statistical and systematic uncertainties, the π0 and η measurements are complementary at high pT; thus, along with the extended pT range of these data they can provide additional constraints for theoretical modeling and the extraction of transport properties.
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(2010) Physical Review D. 82, 1, 012001. Abstract[All authors]
We report the measurement of the transverse momentum dependence of inclusive J/ψ polarization in p+p collisions at √s=200GeV performed by the PHENIX Experiment at the Relativistic Heavy Ion Collider. The J/ψ polarization is studied in the helicity, Gottfried-Jackson, and Collins-Soper frames for pT
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(2010) Physical review letters. 104, 25, 252301. Abstract
Hard-scattered parton probes produced in collisions of large nuclei indicate large partonic energy loss, possibly with collective produced-medium response to the lost energy. We present measurements of π0 trigger particles at transverse momenta pTt=4-12GeV/c and associated charged hadrons (pTa=0.5-7GeV/c) vs relative azimuthal angle Δφ in Au+Au and p+p collisions at √sNN=200GeV. The Au+Au distribution at low pTa, whose shape has been interpreted as a medium effect, is modified for pTt
[All authors] -
(2010) European Physical Journal C. 66, 3, p. 377-386 Abstract
We perform a systematic comparison of the statistical model parametrization of hadron abundances observed in high-energy pp, AA and e+e- collisions. The basic aim of the study is to test if the quality of the description depends on the nature of the collision process. In particular, we want to see if nuclear collisions, with multiple initial interactions, lead to "more thermal" average multiplicities than elementary pp collisions or e+e- annihilation. Such a comparison is meaningful only if it is based on data for the same or similar hadronic species and if the analyzed data has quantitatively similar errors. When these requirements are maintained, the quality of the statistical model description is found to be the same for the different initial collision configurations.
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(2010) Physical review letters. 104, 13, 132301. Abstract[All authors]
The production of e+e- pairs for me+e -
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(2010) Physical Review C. 81, 3, 034911. Abstract[All authors]
PHENIX has measured the e+e- pair continuum in √sNN=200□ GeV Au+Au and p+p collisions over a wide range of mass and transverse momenta. The e+e- yield is compared to the expectations from hadronic sources, based on PHENIX measurements. In the intermediate-mass region, between the masses of the φ and the J/ψ meson, the yield is consistent with expectations from correlated cc□ production, although other mechanisms are not ruled out. In the low-mass region, below the φ, the p+p inclusive mass spectrum is well described by known contributions from light meson decays. In contrast, the Au+Au minimum bias inclusive mass spectrum in this region shows an enhancement by a factor of 4.7±0. 4stat±1.5syst±0.9model. At low mass (mee
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(2010) IEEE Nuclear Science Symposuim and Medical Imaging Conference, NSS/MIC 2010. p. 865-870 Abstract
The PHENIX Hadron Blind Detector (HBD) is a high-performance Cherenkov counter used to detect electrons in relativistic heavy ion collisions at RHIC. A High Voltage Control and Monitoring System (HVC) was developed to provide optimal control over the detector for maximal performance and protection against damage from possible discharges. The HVC comprises several novel hardware components including a voltage divider board and trip detection/protection boards for each power supply module, while actual control of the HV is maintained by a software suite which incorporates Modern Optimal Control Theory and Artificial Intelligence concepts. The software suite is made up of several concurrently operating subsystems, which periodically processes measurements fed back from the HV mainframe, the HBD gas pressure (P) and temperature (T) sensors, analyzes the GEM module behavior in reference to its performance over time, determines a custom response and modifies the HV when necessary. Since the HBD gain is very sensitive to P/T fluctuations, the HVC automatically modifies the GEM/Mesh voltage accordingly in order to keep the gain variations within a nominal operating range of / 10%. Both hardware and software components of the HVC will be described, along with the successful performance results throughout the commissioning pp Run-9 and the HBD's final and most important AuAu Run-10.
2009
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(2009) Nuclear Physics A. 830, p. 757C-760C Abstract
The PHENIX experiment at RHIC has measured the phi-meson production at mid-rapidity in p+p, d+Au, Cu+Cu and Au+Au collisions at root s(NN) = 200 GeV via the K+K- decay mode. The transverse momentum spectra of the phi-meson and the nuclear modification factor as a function of centrality are reviewed here.
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(2009) Physical Review C. 80, 5, 054907. Abstract[All authors]
Measurements of the azimuthal anisotropy of high-pT neutral pion (π0) production in Au+Au collisions at sNN=200 GeV by the PHENIX experiment are presented. The data included in this article were collected during the 2004 Relativistic Heavy Ion Collider running period and represent approximately an order of magnitude increase in the number of analyzed events relative to previously published results. Azimuthal angle distributions of π0 mesons detected in the PHENIX electromagnetic calorimeters are measured relative to the reaction plane determined event-by-event using the forward and backward beam-beam counters. Amplitudes of the second Fourier component (v2) of the angular distributions are presented as a function of π0 transverse momentum (pT) for different bins in collision centrality. Measured reaction plane dependent π0 yields are used to determine the azimuthal dependence of the π0 suppression as a function of pT, RAA(Δ,pT). A jet-quenching motivated geometric analysis is presented that attempts to simultaneously describe the centrality dependence and reaction plane angle dependence of the π0 suppression in terms of the path lengths of hypothetical parent partons in the medium. This set of results allows for a detailed examination of the influence of geometry in the collision region and of the interplay between collective flow and jet-quenching effects along the azimuthal axis.
-
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(2009) Physical review letters. 103, 14, 142301. Abstract
Bose-Einstein correlations of charged kaons are used to probe Au+Au collisions at sNN=200GeV and are compared to charged pion probes, which have a larger hadronic scattering cross section. Three-dimensional Gaussian source radii are extracted, along with a one-dimensional kaon emission source function. The centrality dependences of the three Gaussian radii are well described by a single linear function of Npart1/3 with a zero intercept. Imaging analysis shows a deviation from a Gaussian tail at r10fm, although the bulk emission at lower radius is well described by a Gaussian. The presence of a non-Gaussian tail in the kaon source reaffirms that the particle emission region in a heavy-ion collision is extended, and that similar measurements with pions are not solely due to the decay of long-lived resonances.
[All authors] -
(2009) Physical review letters. 103, 1, 012003. Abstract[All authors]
The double helicity asymmetry in neutral pion production for pT=1 to 12GeV/c was measured with the PHENIX experiment to access the gluon-spin contribution, ΔG, to the proton spin. Measured asymmetries are consistent with zero, and at a theory scale of μ2=4GeV2 a next to leading order QCD analysis gives ΔG[0.02,0.3]=0.2, with a constraint of -0.7
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(2009) Physical Review C. 80, 2, 024908. Abstract[All authors]
We report the observation at the Relativistic Heavy Ion Collider of suppression of back-to-back correlations in the direct photon+jet channel in Au+Au relative to p+p collisions. Two-particle correlations of direct photon triggers with associated hadrons are obtained by statistical subtraction of the decay photon-hadron (γ-h) background. The initial momentum of the away-side parton is tightly constrained, because the parton-photon pair exactly balance in momentum at leading order in perturbative quantum chromodynamics, making such correlations a powerful probe of the in-medium parton energy loss. The away-side nuclear suppression factor, IAA, in central Au+Au collisions, is 0.32±0.12stat±0.09syst for hadrons of 3
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(2009) Physical review letters. 103, 8, 082002. Abstract[All authors]
The momentum distribution of electrons from semileptonic decays of charm and bottom quarks for midrapidity |y|
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(2009) Physical Review C. 80, 2, 024909. Abstract[All authors]
We present inclusive charged hadron elliptic flow (v2) measured over the pseudorapidity range |η|6.5) pseudorapidities and (2) the two-particle cumulant method extracted using correlations between particles detected at midrapidity. The two event-plane results are consistent within systematic uncertainties over the measured pT and in centrality 0-40%. There is at most a 20% difference in the v2 between the two event-plane methods in peripheral (40-60%) collisions. The comparisons between the two-particle cumulant results and the standard event-plane measurements are discussed.
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(2009) European Physical Journal C. 61, 4, p. 835-840 Abstract
The PHENIX experiment at RHIC has measured a variety of light neutral mesons (pi (0), K (S) (0) , eta, omega, eta ('), phi) via multi-particle decay channels over a wide range of transverse momentum. A review of the recent results on the production rates of light mesons in p + p and their nuclear modification factors in d + Au, Cu + Cu and Au + Au collisions at different energies is presented.
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(2009) Journal Of Physics G-Nuclear And Particle Physics. 36, 6, Abstract
Light vector mesons are among the most informative probes to understand the strongly coupled quark-gluon plasma created at the RHIC. The suppression of light mesons at high transverse momentum, compared to expectations from scaled p + p results, reflects the properties of the strongly interacting matter formed. The phi-meson is one of the probes whose systematic measurement in p + p, d + Au and Au + Au collisions can provide useful information about initial and final state effects on particle production. The PHENIX experiment at the RHIC has measured phi-meson production in various systems ranging from p + p, d + Au to Au + Au collisions via both its di-electron and di-kaon decay modes. A summary of PHENIX results on invariant spectra, nuclear modification factor and elliptic flow of the phi-meson is presented here.
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(2009) European Physical Journal C. 61, 4, p. 721-728 Abstract
This article reviews the current status of experimental results obtained in the measurement of light vector mesons produced in proton-proton and heavy ion collisions at different energies. The review is focused on two phenomena related to the light vector mesons; the modification of the spectral shape in search of chiral symmetry restoration and suppression of the meson production in heavy ion collisions. The experimental results show that the spectral shape of light vector mesons are modified compared to the parameters measured in vacuum. The nature and the magnitude of the modification depends on the energy density of the media in which they are produced. The suppression patterns of light vector mesons are different from the measurements of other mesons and baryons. The mechanisms responsible for the suppression of the mesons are not yet understood. Systematic comparison of existing experimental results points to the missing data which may help to resolve the problem.
-
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(2009) 2009 IEEE Nuclear Science Symposium Conference Record, NSS/MIC 2009. p. 1002-1008 Abstract[All authors]
The PHENIX Hadron Blind Detector (HBD) was successfully operated during the 2009 high energy polarized proton run at RHIC. This was the first data taking run after the detector was rebuilt following its first commissioning run in 2007. The detector was operated for several months under actual beam conditions and showed greatly improved performance over the commissioning run. Results are given on the operation of the detector, determination and calibration of the gain using scintillation light produced by charged particles in CF4, stability of the CsI photocathodes, the ability to identify single and double electrons using the signal from Cherenkov light, and the level of sensitivity of the detector to charged hadrons. A description is also given on the methods used to reconstruct the detector that led to its improved performance.
2008
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(2008) Physical review letters. 101, 23, 232301. Abstract[All authors]
For Au+Au collisions at 200 GeV, we measure neutral pion production with good statistics for transverse momentum, pT, up to 20GeV/c. A fivefold suppression is found, which is essentially constant for 5
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(2008) Physical Review C. 78, 4, 044902. Abstract
A comprehensive survey of event-by-event fluctuations of charged hadron multiplicity in relativistic heavy ions is presented. The survey covers Au+Au collisions at sNN=62.4 and 200 GeV, and Cu+Cu collisions at sNN=22.5,62.4, and 200 GeV. Fluctuations are measured as a function of collision centrality, transverse momentum range, and charge sign. After correcting for nondynamical fluctuations due to fluctuations in the collision geometry within a centrality bin, the remaining dynamical fluctuations expressed as the variance normalized by the mean tend to decrease with increasing centrality. The dynamical fluctuations are consistent with or below the expectation from a superposition of participant nucleon-nucleon collisions based upon p+p data, indicating that this dataset does not exhibit evidence of critical behavior in terms of the compressibility of the system. A comparison of the data with a model where hadrons are independently emitted from a number of hadron clusters suggests that the mean number of hadrons per cluster is small in heavy ion collisions.
[All authors] -
(2008) Physical review letters. 101, 12, 122301. Abstract
Yields for J/ψ production in Cu+Cu collisions at sNN=200GeV have been measured over the rapidity range |y|
[All authors] -
(2008) Physical review letters. 101, 8, 082301. Abstract
Measurements in Au+Au collisions at sNN=200GeV of jet correlations for a trigger hadron at intermediate transverse momentum (pT,trig) with associated mesons or baryons at lower pT,assoc indicate strong modification of the away-side jet. The ratio of jet-associated baryons to mesons increases with centrality and pT,assoc. For the most central collisions, the ratio is similar to that for inclusive measurements. This trend is incompatible with in-vacuum fragmentation but could be due to jetlike contributions from correlated soft partons, which recombine upon hadronization.
[All authors] -
(2008) Physical Review C. 78, 1, 014901. Abstract[All authors]
Azimuthal angle (Δ) correlations are presented for a broad range of transverse momentum (0.4
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(2008) Physical Review C. 77, 6, 064907. Abstract[All authors]
The PHENIX experiment has measured the suppression of semi-inclusive single high-transverse-momentum π0's in Au+Au collisions at sNN=200 GeV. The present understanding of this suppression is in terms of energy loss of the parent (fragmenting) parton in a dense color-charge medium. We have performed a quantitative comparison between various parton energy-loss models and our experimental data. The statistical point-to-point uncorrelated as well as correlated systematic uncertainties are taken into account in the comparison. We detail this methodology and the resulting constraint on the model parameters, such as the initial color-charge density dNg/dy, the medium transport coefficient q, or the initial energy-loss parameter ε0. We find that high-transverse-momentum π0 suppression in Au+Au collisions has sufficient precision to constrain these model-dependent parameters at the ±20-25% (one standard deviation) level. These constraints include only the experimental uncertainties, and further studies are needed to compute the corresponding theoretical uncertainties.
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(2008) Physical Review C. 77, 2, 024912. Abstract[All authors]
We present a new analysis of J/ψ production yields in deuteron-gold collisions at sNN=200 GeV using data taken from the PHENIX experiment in 2003 and previously published in S. S. Adler [Phys. Rev. Lett 96, 012304 (2006)]. The high statistics proton-proton J/ψ data taken in 2005 are used to improve the baseline measurement and thus construct updated cold nuclear matter modification factors (RdAu). A suppression of J/ψ in cold nuclear matter is observed as one goes forward in rapidity (in the deuteron-going direction), corresponding to a region more sensitive to initial-state low-x gluons in the gold nucleus. The measured nuclear modification factors are compared to theoretical calculations of nuclear shadowing to which a J/ψ (or precursor) breakup cross section is added. Breakup cross sections of σbreakup=2.8-1. 4+1.7 (2.2-1.5+1.6) mb are obtained by fitting these calculations to the data using two different models of nuclear shadowing. These breakup cross-section values are consistent within large uncertainties with the 4.2±0.5 mb determined at lower collision energies. Projecting this range of cold nuclear matter effects to copper-copper and gold-gold collisions reveals that the current constraints are not sufficient to firmly quantify the additional hot nuclear matter effect.
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(2008) Physical Review C. 77, 1, 011901. Abstract[All authors]
Azimuthal angle (Δ) correlations are presented for charged hadrons from dijets for 0.4
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(2008) Physical Review C. 77, 1, 014905. Abstract[All authors]
We present transverse momentum (pT) spectra of charged hadrons measured in deuteron-gold and nucleon-gold collisions at sNN=200 GeV for four centrality classes. Nucleon-gold collisions were selected by tagging events in which a spectator nucleon was observed in one of two forward rapidity detectors. The spectra and yields were investigated as a function of the number of binary nucleon-nucleon collisions, ν, suffered by deuteron nucleons. A comparison of charged particle yields to those in p+p collisions show that yield per nucleon-nucleon collision saturates with ν for high momentum particles. We also present the charged hadron to neutral pion ratios as a function of pT.
2007
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(2007) Physical Review C. 76, 3, 034903. Abstract
Longitudinal density correlations of produced matter in Au+Au collisions at sNN=200 GeV have been measured from the inclusive charged particle distributions as a function of pseudorapidity window sizes. The extracted αξ parameter, related to the susceptibility of the density fluctuations in the long-wavelength limit, exhibits a nonmonotonic behavior as a function of the number of participant nucleons, Npart. A local maximum is seen at Npart~90, with corresponding energy density based on the Bjorken picture of εBjτ~2.4 GeV/(fm2c) with a transverse area size of 60 fm2. This behavior may suggest a critical phase boundary based on the Ginzburg-Landau framework.
[All authors] -
(2007) Physical Review C. 76, 3, 034904. Abstract[All authors]
Measurements of neutral pion (π0) production at midrapidity in sNN=200 GeV Au+Au collisions as a function of transverse momentum, pT, collision centrality, and angle with respect to reaction plane are presented. The data represent the final π0 results from the PHENIX experiment for the first RHIC Au+Au run at design center-of-mass energy. They include additional data obtained using the PHENIX Level-2 trigger with more than a factor of 3 increase in statistics over previously published results for pT>6 GeV/c. We evaluate the suppression in the yield of high-pT π0's relative to pointlike scaling expectations using the nuclear modification factor RAA. We present the pT dependence of RAA for nine bins in collision centrality. We separately integrate RAA over larger pT bins to show more precisely the centrality dependence of the high-pT suppression. We then evaluate the dependence of the high-pT suppression on the emission angle Δ of the pions with respect to event reaction plane for seven bins in collision centrality. We show that the yields of high-pT π0's vary strongly with Δ, consistent with prior measurements. We show that this variation persists in the most peripheral bin accessible in this analysis. For the peripheral bins we observe no suppression for neutral pions produced aligned with the reaction plane, whereas the yield of π0's produced perpendicular to the reaction plane is suppressed by a factor of ~2. We analyze the combined centrality and Δ dependence of the π0 suppression in different pT bins using different possible descriptions of parton energy loss dependence on jet path-length averages to determine whether a single geometric picture can explain the observed suppression pattern.
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(2007) Physical Review D. 76, 5, 051106. Abstract[All authors]
The PHENIX experiment presents results from the Relativistic Heavy Ion Collider 2005 run with polarized proton collisions at s=200GeV, for inclusive π0 production at midrapidity. Unpolarized cross section results are given for transverse momenta pT=0.5 to 20GeV/c, extending the range of published data to both lower and higher pT. The cross section is described well for pT2GeV/c, by perturbative QCD. Double helicity asymmetries ALL are presented based on a factor of 5 improvement in uncertainties as compared to previously published results, due to both an improved beam polarization of 50%, and to higher integrated luminosity. These measurements are sensitive to the gluon polarization in the proton. Using one representative model of gluon polarization it is demonstrated that the gluon spin contribution to the proton spin is significantly constrained.
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(2007) Physical review letters. 98, 23, 232301. Abstract[All authors]
The PHENIX experiment at the BNL Relativistic Heavy Ion Collider (RHIC) has measured J/ψ production for rapidities -2.2
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(2007) Physical review letters. 98, 23, 232002. Abstract[All authors]
J/ψ production in p+p collisions at √s = 200 GeV has been measured in the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) over a rapidity range of -2.2 u · σJ/ψpp = 178±3stat±53sys±18norm nb.
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(2007) Physical review letters. 98, 23, 232302. Abstract
We present azimuthal angle correlations of intermediate transverse momentum (1-4GeV/c) hadrons from dijets in Cu+Cu and Au+Au collisions at sNN=62.4 and 200 GeV. The away-side dijet induced azimuthal correlation is broadened, non-Gaussian, and peaked away from Δ =π in central and semicentral collisions in all the systems. The broadening and peak location are found to depend upon the number of participants in the collision, but not on the collision energy or beam nuclei. These results are consistent with sound or shock wave models, but pose challenges to Cherenkov gluon radiation models.
[All authors] -
(2007) Physics Letters B. 649, 5-6, p. 359-369 Abstract[All authors]
Correlations between p and over(p, ̄) at transverse momenta typical of enhanced baryon production in Au + Au collisions are reported. The PHENIX experiment has measured same and opposite sign baryon pairs in Au + Au collisions at sqrt(sN N) = 200 GeV. Correlated production of p and over(p, ̄) with the trigger particle from the range 2.5 T T T range rises with increasing centrality, except for the most central collisions, where baryons show a significantly smaller number of associated mesons. These data are consistent with a picture in which hard scattered partons produce correlated p and over(p, ̄) in the pT region of the baryon excess.
-
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(2007) Physical Review C. 75, 5, 051902. Abstract[All authors]
The PHENIX experiment at RHIC has measured the invariant cross section for ω-meson production at midrapidity in the transverse momentum range 2.5
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(2007) Physical review letters. 98, 17, 172302. Abstract[All authors]
The dependence of transverse momentum spectra of neutral pions and η mesons with pT
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(2007) Physical review letters. 98, 17, 172301. Abstract[All authors]
The PHENIX experiment at the BNL Relativistic Heavy Ion Collider (RHIC) has measured electrons with 0.3
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(2007) European Physical Journal A. 31, 4, p. 836-841 Abstract
The production of the low-mass dielectrons is considered to be a powerful tool to study the properties of the hot and dense matter created in the ultra-relativistic heavy-ion collisions. We present the preliminary results on the first measurements of the low-mass dielectron continuum in Au + Au collisions and the phi-meson production measured in Au + Au and d + Au collisions at root s(NN) = 200 GeV performed by the PHENIX experiment.
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(2007) Physical review letters. 98, 13, 132301. Abstract[All authors]
Emission source functions are extracted from correlation functions constructed from charged pions produced at midrapidity in Au+Au collisions at sNN=200GeV. The source parameters extracted from these functions at low kT give first indications of a long tail for the pion emission source. The source extension cannot be explained solely by simple kinematic considerations. The possible role of a halo of secondary pions from resonance emissions is explored.
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(2007) Physical Review C. 75, 2, 024909. Abstract[All authors]
Inclusive transverse momentum spectra of η mesons in the range pTf2-12 GeV/c have been measured at midrapidity (|η|
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(2007) 2007 IEEE Nuclear Science Symposium and Medical Imaging Conference, NSS-MIC. p. 4662-4665 Abstract[All authors]
The Hadron Blind Detector (HBD) is new upgrade detector for the PHENIX experiment at RHIC that consists of a windowless Cherenkov radiator directly coupled to a set of triple Gas Electron Multipliers (GEMs). The individual GEMs measure 22×27 cm2, and the top GEM in the stack is coated with a ∼300 nm layer of CsI that serves as a photocathode. The signal amplitude from the triple GEM stack is used to differentiate between single isolated electrons and overlapping electrons from close pairs. Therefore, the absolute gain of the GEM stack is a crucial parameter in understanding and interpreting the data. We accumulated extensive data on the GEMs during the design and construction of the detector, including gain variation with time, charging effects, saturation, gain uniformity, and source rate dependence. These results, as well as our experience in operating the detector during its first run at RHIC, will be presented at the Workshop.
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(2007) 2007 IEEE Nuclear Science Symposium and Medical Imaging Conference, NSS-MIC. p. 1997-2000 Abstract[All authors]
A Hadron Blind Detector (HBD) has been installed in the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC). A 2300 channel compact 12-bit 60 MHz digitizer system has been built to read the HBD system. The raw signals are shaped with 70 ns rise time and are directly digitized. The time and charge of the raw signals can be calculated from the multiple samples. The system is designed to handle Level 1 (L1) trigger rates up to 25 KHz with 5 L1 event buffers. Large amounts of data are generated after the ADC. Issues regarding clock distribution, data handling, event buffers, and L1 trigger primitive generations have been addressed. The overall system performance will also be discussed.
2006
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(2006) Nuclear Physics A. 774, p. 739-742 Abstract
The properties of the phi-meson have been measured via its e(+)e(-) and K+K- decay channels in Au+Au collisions at root s(NN) = 200 GeV by the PHENIX experiment, The preliminary yields and temperatures derived for the minimum bias and several centrality bins in both decay channels are presented.
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(2006) Physical review letters. 96, 3, 032001. Abstract[All authors]
The invariant differential cross section for inclusive electron production in p+p collisions at s=200GeV has been measured by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider over the transverse momentum range 0.4≤pT≤5.0GeV/c in the central rapidity region (|η|≤0.35). The contribution to the inclusive electron spectrum from semileptonic decays of hadrons carrying heavy flavor, i.e., charm quarks or, at high pT, bottom quarks, is determined via three independent methods. The resulting electron spectrum from heavy-flavor decays is compared to recent leading and next-to-leading order perturbative QCD calculations. The total cross section of charm quark-antiquark pair production is determined to be σcc̄=0.92±0.15(stat) ±0.54(syst)mb.
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(2006) Physical review letters. 96, 1, 012304. Abstract[All authors]
J/ψ production in d+Au and p+p collisions at sNN=200GeV has been measured by the PHENIX experiment at rapidities -2.2
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(2006) Physical review letters. 96, 3, 032301. Abstract[All authors]
The PHENIX experiment has measured midrapidity (|η|
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(2006) Physical Review D. 73, 9, 091102. Abstract[All authors]
We present an improved measurement of the double helicity asymmetry for π0 production in polarized proton-proton scattering at s=200GeV employing the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC). The improvements to our previous measurement come from two main factors: Inclusion of a new data set from the 2004 RHIC run with higher beam polarizations than the earlier run and a recalibration of the beam polarization measurements for the earlier run, which resulted in reduced uncertainties and increased beam polarizations. The results are compared to a Next to Leading Order (NLO) perturbative Quantum Chromodynamics (pQCD) calculation with a range of polarized gluon distributions.
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(2006) Physical review letters. 96, 20, 202301. Abstract[All authors]
Inclusive transverse momentum spectra of η mesons have been measured within pT=2-10GeV/c at midrapidity by the PHENIX experiment in Au+Au collisions at sNN=200GeV. In central Au+Au the η yields are significantly suppressed compared to peripheral Au+Au, d+Au, and p+p yields scaled by the corresponding number of nucleon-nucleon collisions. The magnitude, centrality, and pT dependence of the suppression is common, within errors, for η and π0. The ratio of η to π0 spectra at high pT amounts to 0.40
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(2006) Physical Review C. 73, 5, 054903. Abstract[All authors]
Dihadron correlations at high transverse momentum pT in d+Au collisions at sNN=200 GeV at midrapidity are measured by the PHENIX experiment at the Relativistic Heavy Ion Collider. From these correlations, we extract several structural characteristics of jets: the root-mean-squared transverse momentum of fragmenting hadrons with respect to the jet jT2, the mean sine-squared of the azimuthal angle between the jet axes sin2 jj, and the number of particles produced within the dijet that are associated with a high-pT particle (dN/dxE distributions). We observe that the fragmentation characteristics of jets in d+Au collisions are very similar to those in p+p collisions and that there is little dependence on the centrality of the d+Au collision. This is consistent with the nuclear medium having little influence on the fragmentation process. Furthermore, there is no statistically significant increase in the value of sin2 jj from p+p to d+Au collisions. This constrains the effect of multiple scattering that partons undergo in the cold nuclear medium before and after a hard collision.
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(2006) Physical Review C. 74, 2, 024904. Abstract[All authors]
PHENIX has measured the centrality dependence of midrapidity pion, kaon, and proton transverse momentum distributions in d+Au and p+p collisions at sNN=200 GeV. The p+p data provide a reference for nuclear effects in d+Au and previously measured Au+Au collisions. Hadron production is enhanced in d+Au, relative to independent nucleon-nucleon scattering, as was observed in lower energy collisions. The nuclear modification factor for (anti)protons is larger than that for pions. The difference increases with centrality but is not sufficient to account for the abundance of baryon production observed in central Au+Au collisions at the BNL Relativistic Heavy Ion Collider (RHIC). The centrality dependence in d+Au shows that the nuclear modification factor increases gradually with the number of collisions encountered by each participant nucleon. We also present comparisons with lower energy data as well as with parton recombination and other theoretical models of nuclear effects on particle production.
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(2006) Physical review letters. 96, 22, 222301. Abstract
Deuteron-gold (d+Au) collisions at the Relativistic Heavy Ion Collider provide ideal platforms for testing QCD theories in dense nuclear matter at high energy. In particular, models suggesting strong saturation effects for partons carrying small nucleon momentum fraction (x) predict modifications to jet production at forward rapidity (deuteron-going direction) in d+Au collisions. We report on two-particle azimuthal angle correlations between charged hadrons at forward/backward (deuteron/gold going direction) rapidity and charged hadrons at midrapidity in d+Au and p+p collisions at sNN=200GeV. Jet structures observed in the correlations are quantified in terms of the conditional yield and angular width of away-side partners. The kinematic region studied here samples partons in the gold nucleus with x∼0.1 to ∼0.01. Within this range, we find no x dependence of the jet structure in d+Au collisions.
[All authors] -
(2006) Physical review letters. 97, 5, 052301. Abstract[All authors]
Azimuthal correlations of jet-induced high-pT charged hadron pairs are studied at midrapidity in Au+Au collisions at sNN=200GeV. The distribution of jet-associated partner hadrons (1.0
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(2006) 2006 IEEE Nuclear Science Symposium - Conference Record. p. 1557-1561 Abstract[All authors]
A Hadron Blind Detector (HBD) has been constructed as part of the detector upgrade program for the PHENIX experiment at RHIC. The HBD is a proximity focused windowless Cherenkov detector operated with pure CF4 that will be used to detect single and double electrons in relativistic heavy ion collisions and provide additional rejection power against Dalitz pairs and photon conversions. The detector consists of a 50 cm long radiator directly coupled to a set of triple GEM detectors equipped with CsI photocathodes to detect UY photons produced by electrons emitting Cherenkov light. A full scale prototype of the HBD was built and tested in order to study its performance under beam conditions. Tests with the prototype demonstrated good separation between electrons and hadrons using pulse height discrimination and cluster size. The final detector has now been constructed and installed in PHENIX and is presently undergoing commissioning in preparation for its first round of data taking during the next heavy ion run at RHIC. Results of the beam test of the prototype, as well as on the construction and initial testing of the final detector, are presented in this paper.
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(2006) Physical Review D. 74, 7, 072002. Abstract[All authors]
The properties of jets produced in p+p collisions at s=200GeV are measured using the method of two-particle correlations. The trigger particle is a leading particle from a large transverse momentum jet while the associated particle comes from either the same jet or the away-side jet. Analysis of the angular width of the near-side peak in the correlation function determines the jet-fragmentation transverse momentum jT. The extracted value, jT2 =585±6(stat)±15(sys)MeV/c, is constant with respect to the trigger particle transverse momentum, and comparable to the previous lower s measurements. The width of the away-side peak is shown to be a convolution of jT with the fragmentation variable, z, and the partonic transverse momentum, kT. The z is determined through a combined analysis of the measured π0 inclusive and associated spectra using jet-fragmentation functions measured in e+e- collisions. The final extracted values of kT are then determined to also be independent of the trigger particle transverse momentum, over the range measured, with value of kT2 =2.68±0.07(stat)±0.34(sys)GeV/c.
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(2006) Transversity 2005. p. 68-76 Abstract[All authors]
The Relativistic Heavy Ion Collider (RHIC), as the world's first and only polarized proton collider, offers a unique environment in which to study the spin structure of the proton. In order to study the proton's transverse spin structure, the PHENIX experiment at RHIC took data with transversely polarized beams in 2001-02 and 2005, and it has plans for further running with transverse polarization in 2006 and beyond. Results from early running as well as prospective measurements for the future will be discussed.
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(2006) Physical review letters. 96, 3, 032302. Abstract[All authors]
The azimuthal distribution of identified π0 and inclusive photons has been measured in sNN=200GeV Au+Au collisions with the PHENIX experiment at the Relativistic Heavy-Ion Collider (RHIC). The second-harmonic parameter (v2) was measured to describe the observed anisotropy of the azimuthal distribution. The measured inclusive photon v2 is consistent with the value expected for the photons from hadron decay and is also consistent with the lack of direct photon signal over the measured pT range 1-6GeV/c. An attempt is made to extract v2 of direct photons.
2005
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(2005) Nuclear Physics A. 757, 1-2 SPEC. ISS., p. 184-283 Abstract[All authors]
Extensive experimental data from high-energy nucleus-nucleus collisions were recorded using the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC). The comprehensive set of measurements from the first three years of RHIC operation includes charged particle multiplicities, transverse energy, yield ratios and spectra of identified hadrons in a wide range of transverse momenta (pT), elliptic flow, two-particle correlations, nonstatistical fluctuations, and suppression of particle production at high pT. The results are examined with an emphasis on implications for the formation of a new state of dense matter. We find that the state of matter created at RHIC cannot be described in terms of ordinary color neutral hadrons.
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(2005) Physical Review C. 72, 2, Abstract[All authors]
The transverse momentum dependence of the azimuthal anisotropy parameter v(2), the second harmonic of the azimuthal distribution, for electrons at midrapidity (vertical bar eta vertical bar
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(2005) European Physical Journal C. 43, 4-Jan, p. 317-322 Abstract
The PHENIX experiment at RHIC has observed a large enhancement of baryon and anti-baryon production at p(T) approximate to 2-5 GeV/c, compared to expectations from jet fragmentation. While a number of theoretical interpretations of the data are available, there is not yet a definitive answer to the "baryon puzzle". We investigate the centrality dependence of phi-meson production at mid-rapidity in Au+Au collisions with root s(NN) = 200 GeV. Comparison with the proton and anti-proton spectra reveal similar shapes, as expected for soft production described by hydrodynamics. However, the absolute yields show a different centrality dependence. The nuclear modi. cation factors for phi are similar to those of pions, rather than (anti) protons that have similar mass. At intermediate p(T), baryon/meson effects seem to be more important than the mass effects, in support of recombination models.
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(2005) European Physical Journal C. 43, 4-Jan, p. 271-280 Abstract
Results from the PHENIX experiment of measurements of high-p(T) particle production presented at the Hard Probes 2004 Conference are summarized. This paper focuses on a sub-set of the measurements presented at the conference, namely the suppression of pi(0) production at moderate to high p(T) as a function of angle with respect to the collision reaction plane, Delta phi, for different collision centralities. The data are presented in the form of nuclear modi. cation factor as a function of angle with respect to the reaction plane, R-AA(Delta phi). The data are analyzed using empirical estimates of the medium-induced energy loss obtained from the R-AA(Delta phi) values. A geometric analysis is performed with the goal of understanding the simultaneous dependence of R-AA on Delta phi and centrality. We find that the centrality and Delta phi dependence of the pi(0) suppression can be made approximately consistent using an admittedly over-simplistic description of the geometry of the jet propagation in the medium but only if the energy loss is effectively reduced for short parton path lengths in the medium. We find that with a more "canonical" treatment of the quenching geometry, the pi(0) suppression varies more rapidly with Delta phi than would be expected from the centrality dependence of the suppression.
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(2005) European Physical Journal C. 43, 4-Jan, p. 201-208 Abstract
The PHENIX experiment at RHIC measured single electron spectra in p+p, d+Au and Au+Au collisions at root s(NN) = 200 GeV, and in Au+Au collisions at root s(NN) = 62.4 GeV. In these spectra, electrons from semi-leptonic decays of charmed particles are the dominant contribution after subtraction of all 'photonic' sources ( photon conversions, Dalitz decays, decays of light vector mesons). The p+p open charm production cross-section is found to be in good agreement with pQCD NLO calculations. The shape of the distributions obtained for p+p interactions is compared with those observed for nucleus-nucleus collisions. From p+p to d+Au and Au+Au interactions, open charm production is found to scale with the number of binary collisions N-coll. Au+Au data at root s(NN) = 62.4 GeV is compatible with the ISR p+p results scaled by Ncoll. The elliptic flow parameter v(2) of heavy flavor electrons has also been measured, and is found to be non-zero in the intermediate p(T) range.
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(2005) European Physical Journal C. 43, 4-Jan, p. 421-426 Abstract
Recent results on low mass dilepton measurements from the PHENIX experiment are reported. Invariant mass spectra of phi -> e(+)e(-) are measured for the first time in Au-Au collisions at root sNN = 200 GeV in Run2. In d-Au collisions, the yields and M-T slopes of both phi -> e(+)e(-) and phi -> K+K- are measured. Both results are consistent with each other within errors. In the future, a Hadron Blind Detector will be installed in PHENIX which will enhance our capabilities of rejecting external photon conversions and Dalitz pairs, that will result in a significant reduction of the large combinatorial background.
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(2005) European Physical Journal C. 43, 4-Jan, p. 303-310 Abstract
Transverse momentum (p(T)) spectra measured by the PHENIX experiment at RHIC in Au+Au, d+Au and pp collisions at root s(NN) = 200 GeV and in Au+Au collisions at root s(NN) = 62.4 GeV are presented. A suppression of the yield of high pT hadrons in central Au+Au collisions by a factor 4 - 5 at p(T) > 5 GeV/ c is found relative to the pp reference scaled by the nuclear overlap function . In contrast, direct photons are not suppressed in central Au+Au collisions and no suppression of high pT particles can be seen in d+Au collisions. This leads to the conclusion that the dense medium formed in central Au+Au collisions is responsible for the suppression.
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(2005) Physical Review C - Nuclear Physics. 72, 2, 024901. Abstract[All authors]
The transverse momentum dependence of the azimuthal anisotropy parameter v2, the second harmonic of the azimuthal distribution, for electrons at midrapidity (|η|
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(2005) European Physical Journal C. 43, 4-Jan, p. 173-178 Abstract
The PHENIX experiment measured J/psi production in pp, d+Au and Au+Au reactions at root s(NN) = 200 GeV over a wide range of rapidity and transverse momentum. The nuclear modi. cation factor obtained by comparing the d+Au and pp cross sections as a function of rapidity, is consistent with shadowing of the gluon distribution functions. J/psi production in Au+Au collisions was compared to the production in pp collisions and it was found to be inconsistent with models that predict strong enhancement relative to binary collision scaling.
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(2005) Nuclear Instruments & Methods In Physics Research Section A-Accelerators Spectrometers Detectors And Associated Equipment. 546, 3, p. 466-480 Abstract[All authors]
A Hadron Blind Detector (HBD) is being developed for the PHENIX experiment at RHIC. It consists of a Cherenkov radiator operated with pure CF4 directly coupled in a windowless configuration to a triple-GEM detector element with a CsI photocathode and pad readout. The HBD operates in the bandwidth 6-11.5 eV (110-200 nm). We studied the detector response to minimum ionizing particles and to electrons. We present measurements of the CsI quantum efficiency, which are in very good agreement with previously published results over the bandwidth 6-8.3 eV and extend them up to 10.3 eV. Discharge probability and aging studies of the GEMs and the CsI photocathode in pure CF4 are presented.
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(2005) Physical Review C. 72, 1, 014903. Abstract[All authors]
We present the results of I meson production in the K+K- decay channel from Au+Au collisions at sNN=200GeV as measured at midrapidity by the PHENIX detector at Brookhaven National Laboratory's Relativistic Heavy Ion Collider. Precision resonance centroid and width values are extracted as a function of collision centrality. No significant variation from the Particle Data Group accepted values is observed, contrary to some model predictions. The I transverse mass spectra are fitted with a linear exponential function for which the derived inverse slope parameter is seen to be constant as a function of centrality. However, when these data are fitted by a hydrodynamic model the result is that the centrality-dependent freeze-out temperature and the expansion velocity values are consistent with the values previously derived from fitting identified charged hadron data. As a function of transverse momentum the collisions scaled peripheral-to-central yield ratio RCP for the I is comparable to that of pions rather than that of protons. This result lends support to theoretical models that distinguish between baryons and mesons instead of particle mass for explaining the anomalous (anti) proton yield.
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(2005) Physical Review Letters. 94, 23, Abstract
New measurements are presented for charged hadron azimuthal correlations at midrapidity in Au+Au collisions at root s(NN)=62.4 and 200 GeV. They are compared to earlier measurements obtained at root s(NN)=130 GeV and in Pb+Pb collisions at root s(NN)=17.2 GeV. Sizeable anisotropies are observed with centrality and transverse momentum (p(T)) dependence characteristic of elliptic flow (v(2)). For a broad range of centralities, the observed magnitudes and trends of the differential anisotropy, v(2)(p(T)), change very little over the collision energy range root s(NN)=62-200 GeV, indicating saturation of the excitation function for v(2) at these energies. Such a saturation may be indicative of the dominance of a very soft equation of state for root s(NN)similar to 60-200 GeV.
[All authors] -
(2005) Physical Review Letters. 94, 23, Abstract[All authors]
The first measurement of direct photons in Au+Au collisions at root s(NN)=200 GeV is presented. The direct photon signal is extracted as a function of the Au+Au collision centrality and compared to next-to-leading order perturbative quantum chromodynamics calculations. The direct photon yield is shown to scale with the number of nucleon-nucleon collisions for all centralities.
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(2005) Physical Review C. 71, 5, 051902. Abstract
Two particle correlations between identified meson and baryon trigger particles with 2.5
[All authors] -
(2005) Physical review D. 71, 7, p. 1-7 071102. Abstract
A measurement of direct photons in p + p collisions at √s = 200 GeV is presented. A photon excess above background from π0 → γ + γ, η → γ + γ and other decays is observed in the transverse momentum range 5.5 pT
[All authors] -
(2005) Physical Review Letters. 94, 12, Abstract[All authors]
The production of deuterons and antideuterons in the transverse momentum range 1.1
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(2005) Physical Review Letters. 94, 8, Abstract[All authors]
We report on charged hadron production in deuteron-gold reactions at roots(NN) = 200 GeV. Our measurements in the deuteron direction cover 1.4
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(2005) Physical Review C. 71, 3, 034908. Abstract[All authors]
The PHENIX experiment at the relativistic heavy ion collider (RHIC) has measured transverse energy and charged particle multiplicity at midrapidity in Au + Au collisions at center-of-mass energies √SNN = 19.6, 130, and 200 GeV as a function of centrality. The presented results are compared to measurements from other RHIC experiments and experiments at lower energies. The √SNN dependence of dET/dη and dN ch/dη per pair of participants is consistent with logarithmic scaling for the most central events. The centrality dependence of dE T/dη and dNch/dη is similar at all measured incident energies. At RHIC energies, the ratio of transverse energy per charged particle was found to be independent of centrality and growing slowly with √SNN. A survey of comparisons between the data and available theoretical models is also presented.
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(2005) Physical Review Letters. 94, 8, Abstract[All authors]
The PHENIX experiment has measured midrapidity transverse momentum spectra (0.4
2004
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(2004) Physical review letters. 93, 20, p. 202002-1-202002-6 202002. Abstract
A technique for determining the polarized gluon distribution using polarized protons, was presented. The transverse beam polarization was measured in Relativistic Heavy Ion Collider (RHIC) independently in each beam using proton-carbon elastic scattering in the Coulomb nuclear interference region. The results of the double spin helicity asymmetries for π0 production began to probe the proton spin structure in the perturbative quantum chromodynamic (QCD) regime with a sensitivity comparable to the polarized inclusive deep inelastic scattering data. The observed symmetry was small and was compared to a next-to-leading-order perturbative (NLO pQCD) calculation with a range of polarized gluon distributions.
[All authors] -
(2004) Physical review letters. 93, 15, p. 152302-1-152302-6 152302. Abstract[All authors]
The use of PHENIX experiment at midrapidity in Au + Au collision at √sNN = 200 GeV for calculating Bose-Einstein correlation of identical charged ion pairs was discussed. It was found that the Bertsch-Partt radius parameters were determined as a function of the transverse momentum of the pair and as function of the collision. It was also observed that the value of Rout/Rside, as function of kT decrease from ∼1.1 to ∼ 0.8 over the range of kT. The results show that the measurements of the transverse momentum dependence of the HBT radii.
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(2004) Physical review letters. 93, 9, p. 092301-1-092301-6 092301. Abstract[All authors]
The event-by-event fluctuations of the average transverse momentum of produced particles near mid-rapidity were measured using the PHENIX Collaboration in √SNN=20GeV Au + Au, and p+p collisions at the Relativistic Heavy Ion Collider. The fluctuations were in excess of the expectation for statistically independent particle emission for all centralities. The dependence on both, the centrality of the collision and on the pT range, over which the average is calculated, were exhibited by excess fluctuations. It is found that simulation of random particle production with addition of contributions from hard-scattering processes produces both, the centrality and pT dependence.
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(2004) Physical Review C. 69, 3, p. 034909-1-034909-32 034909. Abstract[All authors]
The centrality dependence of transverse momentum distributions and yields for π±,K±, p, and p in Au +Au collisions at √sNN=200 GeV at midrapidity are measured by the PHENIX experiment at the Relativistic Heavy Ion Collider. We observe a clear particle mass dependence of the shapes of transverse momentum spectra in central collisions below ∼2 GeV/c in pT. Both mean transverse momenta and particle yields per participant pair increase from peripheral to midcentral and saturate at the most central collisions for all particle species. We also measure particle ratios of π-/π+, K -/K+, ̄p/p, K/π, p/π, and ̄p/π as a function of pT and collision centrality. The ratios of equal mass particle yields are independent of pT and centrality within the experimental uncertainties. In central collisions at intermediate transverse momenta ∼1.5-4.5 GeV/c, proton and antiproton yields constitute a significant fraction of the charged hadron production and show a scaling behavior different from that of pions.
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(2004) Physical Review C. 69, 3, p. 034910-1-034910-20 034910. Abstract[All authors]
The PHENIX experiment at the Relativistic Heavy Ion Collider has measured charged hadron yields at midrapidity over a wide range of transverse momenta (0.5
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(2004) Physical Review C - Nuclear Physics. 69, 2, p. 249041-2490429 024904. Abstract[All authors]
Transverse momentum spectra and yields of hadrons are measured by the PHENIX collaboration in Au +Au collisions at √SNN=130 GeV at the Relativistic Heavy Ion Collider. The time-of-flight resolution allows identification of pions to transverse momenta of 2 GeV/c and protons and antiprotons to 4 GeV/c. The yield of pions rises approximately linearly with the number of nucleons participating in the collision, while the number of kaons, protons, and antiprotons increases more rapidly. The shape of the momentum distribution changes between peripheral and central collisions. Simultaneous analysis of all the pT spectra indicates radial collective expansion, consistent with predictions of hydrodynamic models. Hydrodynamic analysis of the spectra shows that the expansion velocity increases with collision centrality and collision energy. This expansion boosts the particle momenta, causing the yield from soft processes to exceed that for hard to large transverse momentum, perhaps as large as 3 GeV/c.
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(2004) Physical review letters. 92, 5, p. 518021-518026 051802. Abstract[All authors]
The production of Jψ, measured in proton-proton collisions at √s=200 GeV is discussed. Distributions of the transverse momentum and rapidity, along with the measurements of the mean transverse momentum and total production cross section are presented. It is found that the total J/ψ cross section is 4.0±0.6(stat)±0.6(syst)±0.4(abs) μb. Results show that the mean transverse momentum is 1.80±0.23(stat)±0.16(syst) GeV/c.
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(2004) Physical Review C - Nuclear Physics. 69, 2, p. 29 Abstract[All authors]
Transverse momentum spectra and yields of hadrons are measured by the PHENIX collaboration in [Formula Presented] collisions at [Formula Presented] at the Relativistic Heavy Ion Collider. The time-of-flight resolution allows identification of pions to transverse momenta of [Formula Presented] and protons and antiprotons to [Formula Presented]. The yield of pions rises approximately linearly with the number of nucleons participating in the collision, while the number of kaons, protons, and antiprotons increases more rapidly. The shape of the momentum distribution changes between peripheral and central collisions. Simultaneous analysis of all the [Formula Presented] spectra indicates radial collective expansion, consistent with predictions of hydrodynamic models. Hydrodynamic analysis of the spectra shows that the expansion velocity increases with collision centrality and collision energy. This expansion boosts the particle momenta, causing the yield from soft processes to exceed that for hard to large transverse momentum, perhaps as large as [Formula Presented].
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(2004) Physical Review C - Nuclear Physics. 69, 1, p. 149011-1490110 014901. Abstract[All authors]
First results on charm quarkonia production in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) are presented. The yield of J/ψ's measured in the PHENIX experiment via electron-positron decay pairs at midrapidity for Au-Au reactions at √SNN=200 GeV is analyzed as a function of collision centrality. For this analysis we have studied 49.3 × 106 minimum bias Au-Au reactions. We present the J/ψ invariant yield dN/dy for peripheral and midcentral reactions. For the most central collisions where we observe no signal above background, we quote 90% confidence level upper limits. We compare these results with our J/ψ measurement from proton-proton reactions at the same energy. We find that our measurements are not consistent with models that predict strong enhancement relative to binary collision scaling.
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(2004) Physical review letters. 92, 5, p. 6 Abstract[All authors]
[Formula presented] production has been measured in proton-proton collisions at [Formula presented] over a wide rapidity and transverse momentum range by the PHENIX experiment at the Relativistic Heavy Ion Collider. Distributions of the rapidity and transverse momentum, along with measurements of the mean transverse momentum and total production cross section are presented and compared to available theoretical calculations. The total [Formula presented] cross section is [Formula presented]. The mean transverse momentum is [Formula presented].
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A hadron blind detector for the PHENIX experiment at RHIC(2004) IEEE Nuclear Science Symposium Conference Record. 2, p. 1137-1141 N25-1. Abstract[All authors]
A Hadron Blind Detector (HBD) is being developed for an upgrade of the PHENIX experiment at RHIC. The HBD is a windowless Cherenkov detector, operated with pure CF 4 in a special proximity focus configuration. The detector consists of a 50cm long radiator, directly coupled to a triple GEM detector which has a Csl photocathode evaporated on the top surface of the upper-most GEM foil, and a pad readout at the bottom of the GEM stack. Detailed studies of the detector performance, including hadron rejection, figure of merit, N 0, number of photoelectrons and efficiency are presented. These studies include measurements performed with a UV lamp, an 55Fe x-ray source and an 241Am alpha source. Results will also be given on aging studies of the GEM foils and the CsI photocathode in pure CF 4.
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(2004) Physical Review C. 69, 1, Abstract[All authors]
First results on charm quarkonia production in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) are presented. The yield of [Formula Presented]s measured in the PHENIX experiment via electron-positron decay pairs at midrapidity for [Formula Presented] reactions at [Formula Presented] is analyzed as a function of collision centrality. For this analysis we have studied [Formula Presented] minimum bias [Formula Presented] reactions. We present the [Formula Presented] invariant yield [Formula Presented] for peripheral and midcentral reactions. For the most central collisions where we observe no signal above background, we quote [Formula Presented] confidence level upper limits. We compare these results with our [Formula Presented] measurement from proton-proton reactions at the same energy. We find that our measurements are not consistent with models that predict strong enhancement relative to binary collision scaling.
2003
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(2003) Physical review letters. 91, 24, Abstract[All authors]
The invariant differential cross section for inclusive neutral-pion production in [Formula presented] collisions at [Formula presented] has been measured at midrapidity ([Formula presented]) over the range [Formula presented] by the PHENIX experiment at the Relativistic Heavy Ion Collider. Predictions of next-to-leading order perturbative QCD calculations are consistent with these measurements. The precision of our result is sufficient to differentiate between prevailing gluon-to-pion fragmentation functions.
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(2003) Physical review letters. 91, 24, p. 241803/1-241803/6 241803. Abstract[All authors]
The invariant differential cross section for inclusive neutral-pion production in p+p collisions at √s=200 GeV was measured at midrapidity (|η|
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(2003) Physical review letters. 91, 17, Abstract[All authors]
We report on the yield of protons and antiprotons, as a function of centrality and transverse momentum, in [Formula presented] collisions at [Formula presented] measured at midrapidity by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider. In central collisions at intermediate transverse momenta ([Formula presented]) a significant fraction of all produced particles are protons and antiprotons. They show a centrality-scaling behavior different from that of pions. The [Formula presented] and [Formula presented] ratios are enhanced compared to peripheral [Formula presented], [Formula presented], and [Formula presented] collisions. This enhancement is limited to [Formula presented] as deduced from the ratio of charged hadrons to [Formula presented] measured in the range [Formula presented].
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(2003) Physical review letters. 91, 17, p. 1723011-1723016 172301. Abstract[All authors]
We report on the yield of protons and antiprotons, as a function of centrality and transverse momentum, in Au+Au collisions at √sNN=200\u200a\u200aGeV
measured at midrapidity by the PHENIX experiment at the BNL
Relativistic Heavy Ion Collider. In central collisions at intermediate
transverse momenta (1.5 -
(2003) Physical review letters. 91, 7, Abstract[All authors]
Transverse momentum spectra of neutral pions in the range [Formula presented] have been measured at midrapidity by the PHENIX experiment at BNL RHIC in [Formula presented] collisions at [Formula presented]. The [Formula presented] multiplicity in central reactions is significantly below the yields measured at the same [Formula presented] in peripheral [Formula presented] and [Formula presented] reactions scaled by the number of nucleon-nucleon collisions. For the most central bin, the suppression factor is [Formula presented] at [Formula presented] and increases to [Formula presented] at [Formula presented]. At larger [Formula presented], the suppression remains constant within errors. The deficit is already apparent in semiperipheral reactions and increases smoothly with centrality.
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(2003) Physical review letters. 91, 7, p. 723031-723036 072303. Abstract[All authors]
The measurement of transverse momentum spectra of neutral pions with p T
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(2003) Physical review letters. 91, 7, p. 723011-723016 072301. Abstract[All authors]
The measurement of transverse momentum spectra of the neutral pions in Au + Au collisions was discussed. It was found that the π0 multiplicity of the central reactions was significantly below the yields measured in p + p and Au + Au reactions. It was also found that this deficit increased smoothly with the centrality and was present in the semiperipheral reactions.
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(2003) Physical review letters. 91, 7, Abstract[All authors]
Transverse momentum spectra of charged hadrons with [Formula presented] and neutral pions with [Formula presented] have been measured at midrapidity by the PHENIX experiment at BNL RHIC in [Formula presented] collisions at [Formula presented]. The measured yields are compared to those in [Formula presented] collisions at the same [Formula presented] scaled up by the number of underlying nucleon-nucleon collisions in [Formula presented]. The yield ratio does not show the suppression observed in central [Formula presented] collisions at RHIC. Instead, there is a small enhancement in the yield of high momentum particles.
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(2003) Physical review letters. 91, 4, Abstract[All authors]
We report on first measurements of low-mass electron-positron pairs in Pb-Au collisions at the CERN SPS beam energy of [Formula presented]. The observed pair yield integrated over the range of invariant masses [Formula presented] is enhanced over the expectation from neutral meson decays by a factor of [Formula presented], somewhat larger than previously observed at the higher energy of [Formula presented]. The results are discussed with reference to model calculations based on [Formula presented] annihilation with a modified [Formula presented] propagator. They may be linked to chiral symmetry restoration and support the notion that the in-medium modifications of the [Formula presented] are more driven by baryon density than by temperature.
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(2003) Physics Letters B. 561, 1-2, p. 82-92 Abstract[All authors]
PHENIX has measured the centrality dependence of charged hadron pT spectra from Au + Au collisions at sNN√ = 130 GeV. The truncated mean pT decreases with centrality for pT > 2 GeV/c, indicating an apparent reduction of the contribution from hard scattering to high pT hadron production. For central collisions the yield at high pT is shown to be suppressed compared to binary nucleon-nucleon collision scaling of p + p data. This suppression is monotonically increasing with centrality, but most of the change occurs below 30% centrality, i.e., for collisions with less than ∼ 140 participating nucleons. The observed pT and centrality dependence is consistent with the particle production predicted by models including hard scattering and subsequent energy loss of the scattered partons in the dense matter created in the collisions.
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(2003) Nuclear Instruments & Methods In Physics Research Section A-Accelerators Spectrometers Detectors And Associated Equipment. 502, 1, p. 200-204 Abstract[All authors]
A Hadron Blind Detector (HBD) is proposed as upgrade of the PHENIX detector at RHIC, BNL. The HBD will allow the measurement of low-mass e+e- pairs from the decay of the light vector mesons ρ, ω, φ and the low-mass continuum- in Au-Au collisions at √sNN = 200 GeV. From general considerations, the HBD has to identify electrons with a high efficiency (>90%) and with a double hit resolution better than 90%, it must have a pion rejection factor of at least 200 and a radiation budget of the order of 1% of a radiation length. The choice that emerges is a windowless Cherenkov detector, operated with a CF4 based gas mixture in a special proximity focus configuration with a CsI cathode evaporated on GEMs. Published by Elsevier Science B.V.
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(2003) PRAMANA-JOURNAL OF PHYSICS. 60, 4, p. 639-650 Abstract
Keywords: CENTRALITY DEPENDENCE; TRANSVERSE ENERGY; MULTIPLICITY; PARTICLE; QCD
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(2003) Nuclear Instruments & Methods In Physics Research Section A-Accelerators Spectrometers Detectors And Associated Equipment. 499, 2-3, p. 469-479 Abstract[All authors]
The PHENIX detector is designed to perform a broad study of A-A, p-A, and p-p collisions to investigate nuclear matter under extreme conditions. A wide variety of probes, sensitive to all timescales, are used to study systematic variations with species and energy as well as to measure the spin structure of the nucleon. Designing for the needs of the heavy-ion and polarized-proton programs has produced a detector with unparalleled capabilities. PHENIX measures electron and muon pairs, photons, and hadrons with excellent energy and momentum resolution. The detector consists of a large number of subsystems that are discussed in other papers in this volume. The overall design parameters of the detector are presented.
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(2003) Nuclear Physics A. 715, p. 494C-497C Abstract
The phi meson is an important probe for studying relativistic heavy ion collisions. Since the mass of the phi meson is close to twice the kaon mass, any medium modification of its spectral shape (mass and/or width) [1] as chiral symmetry restoration is approached may induce a change in its branching ratio in the kaon channel. The simultaneous measurement of phi decay into K+K- and e(+)e(-) is a very powerful tool in the search for such in-medium of s (s) over bar, the phi meson is also a sensitive probe of strangeness modifications. Consisting phi production [2]. The PHENIX experiment at RHIC, with its excellent mass resolution and particle identification capability, (comparable to or better than the natural width of the phi meson) has the unique capability to measure the phi meson through both K+K- and e(+)e(-) decay channels at mid-rapidity. We present the preliminary results of the phi meson measurement made during the 2001 RHIC run.
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(2003) Physical review letters. 91, 18, Abstract[All authors]
The anisotropy parameter ([Formula presented]), the second harmonic of the azimuthal particle distribution, has been measured with the PHENIX detector in [Formula presented] collisions at [Formula presented] for identified and inclusive charged particle production at central rapidities ([Formula presented]) with respect to the reaction plane defined at high rapidities ([Formula presented]). We observe that the [Formula presented] of mesons falls below that of (anti)baryons for [Formula presented], in marked contrast to the predictions of a hydrodynamical model. A quark-coalescence model is also investigated.
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(2003) Physical review letters. 90, 2, p. 4 Abstract[All authors]
Based on an evaluation of data on pion interferometry and on particle yields at midrapidity, we propose a universal condition for thermal freeze-out of pions in heavy-ion collisions. We show that freeze-out occurs when the mean free path of pions [Formula presented] reaches a value of about 1 fm, which is much smaller than the spatial extent of the system at freeze-out. This critical mean free path is independent of the centrality of the collision and beam energy from the Alternating Gradient Synchrotron to the Relativistic Heavy Ion Collider.
2002
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(2002) Physical review letters. 89, 21, Abstract[All authors]
Two-particle azimuthal correlation functions are presented for charged hadrons produced in [Formula presented] collisions at the Relativistic Heavy Ion Collider ([Formula presented]). The measurements permit determination of elliptic flow without event-by-event estimation of the reaction plane. The extracted elliptic flow values ([Formula presented]) show significant sensitivity to both the collision centrality and the transverse momenta of emitted hadrons, suggesting rapid thermalization and relatively strong velocity fields. When scaled by the eccentricity of the collision zone [Formula presented], the scaled elliptic flow shows little or no dependence on centrality for charged hadrons with relatively low [Formula presented]. A breakdown of this [Formula presented] scaling is observed for charged hadrons with [Formula presented].
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(2002) Physical review letters. 89, 21, p. 2123011-2123016 212301. Abstract[All authors]
The elliptic flow measurements via two-particle azimuthal correlations in Au + Au collisions at the relativistic heavy ion collider were studied. These measurements allowed to obtain the elliptic flow without event-by-event estimation of the reaction plane. It was found that the elliptic flow showed significant senstivity to both the collision centrality and the transverse momenta of emitted hadrons, suggesting rapid thermalization and strong velocity fields.
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(2002) Physical review letters. 89, 8, p. 082301/1-082301/6 082301. Abstract[All authors]
The results from an analysis of net charge fluctuations for particles produced in Au+Au interactions at √sNN=130 GeV. The fluctuations are studied in the variables R=n+/n-, the ratio between positive and negative particles, and Q=n+-n-, the net charge. This paper discusses the advantages and disadvantages of these variables.
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(2002) Physical review letters. 89, 9, p. 923021-923026 092302. Abstract[All authors]
The measurement by the PHENIX experiment at the relativistic heavy ion collider (RHIC) was reported. The transverse momentum spectra were measured for minimum bias and for the 5% most central events. The net baryon numbers were indicative of the baryon transport mechanism in relativistic heavy ion (RHI) collisions. The measured net baryon density was found larger than that predicted by models based on hadronic strings indicating enhanced baryon stopping.
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(2002) Physical review letters. 89, 9, Abstract[All authors]
We present results on the measurement of [Formula presented] and [Formula presented] production in [Formula presented] collisions at [Formula presented] with the PHENIX detector at the Relativistic Heavy Ion Collider. The transverse momentum spectra were measured for minimum bias and for the 5% most central events. The [Formula presented] ratios are constant as a function of [Formula presented] and the number of participants. The measured net [Formula presented] density is significantly larger than predicted by models based on hadronic strings (e.g., HIJING) but in approximate agreement with models which include the gluon-junction mechanism.
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(2002) Physical Review C. 66, 2, 024901. Abstract
Distributions of event-by-event fluctuations of the mean transverse momentum and mean transverse energy near mid-rapidity have been measured in Au+Au collisions at √SNN= 130 GeV at the Relativistic Heavy-Ion Collider. By comparing the distributions to what is expected for statistically independent particle emission, the magnitude of nonstatistical fluctuations in mean transverse momentum is determined to be consistent with zero. Also, no significant nonrandom fluctuations in mean transverse energy are observed. By constructing a fluctuation model with two event classes that preserve the mean and variance of the semi-inclusive PT or eT spectra, we exclude a region of fluctuations in √SNN= 130 GeV Au+Au collisions.
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(2002) Physical review letters. 89, 8, Abstract[All authors]
Data from [Formula presented] interactions at [Formula presented], obtained with the PHENIX detector at the Relativistic Heavy-Ion Collider, are used to investigate local net charge fluctuations among particles produced near midrapidity. According to recent suggestions, such fluctuations may carry information from the quark-gluon plasma. This analysis shows that the fluctuations are dominated by a stochastic distribution of particles, but are also sensitive to other effects, like global charge conservation and resonance decays.
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(2002) Journal Of Physics G-Nuclear And Particle Physics. 28, 7, p. 1861-1868 340. Abstract[All authors]
During the 1999 lead run, CERES has measured hadron and electron-pair production at 40 A GeV/c beam momentum with the spectrometer upgraded by the addition of a radial TPC. Here the analysis of Λ and Λ̄ will be presented.
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(2002) Physical review letters. 88, 24, p. 2423011-2423016 242301. Abstract[All authors]
An intriguing new behavior was reported in elementary hadron production at relativistic heavy ion collider (RHIC). In central Au-Au collisions the antiprotons yield was comparable to the π- at high transverse momentum. The results showed that the transverse energy density and particle multiplicities were higher than the previously observed multiplicities in the relativistic heavy-ion collisions.
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(2002) Physical review letters. 88, 24, p. 6 Abstract[All authors]
Identified [Formula presented], [Formula presented], [Formula presented], and [Formula presented] transverse momentum spectra at midrapidity in [Formula presented] collisions were measured by the PHENIX experiment at RHIC as a function of collision centrality. Average transverse momenta increase with the number of participating nucleons in a similar way for all particle species. Within errors, all midrapidity particle yields per participant are found to be increasing with the number of participating nucleons. There is an indication that [Formula presented], [Formula presented], and [Formula presented] yields per participant increase faster than the [Formula presented] yields. In central collisions at high transverse momenta [Formula presented], [Formula presented] and [Formula presented] yields are comparable to the [Formula presented] yields.
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(2002) Physical review letters. 88, 19, p. 6 Abstract[All authors]
Two-pion correlations in [Formula presented] [Formula presented] collisions at RHIC have been measured over a broad range of pair transverse momentum [Formula presented] by the PHENIX experiment at RHIC. The [Formula presented] dependent transverse radii are similar to results from heavy-ion collisions at [Formula presented], 4.9, and 17.3 GeV, whereas the longitudinal radius increases monotonically with beam energy. The ratio of the outwards to sidewards transverse radii [Formula presented] is consistent with unity and independent of [Formula presented].
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(2002) Physical review letters. 88, 19, p. 1923021-1923026 192302. Abstract[All authors]
Two-pion correlations in Au + Au collisions at realistic heavy ion collidors (RHIC) were measured. The transverse momentum kT dependent transverse radii were similar to results from heavy-ion collisions at √sNN = 4.1, 4.9 and 17.3 GeV. With beam energy the longitudinal radius increased monotonically. The ratio of the outwards to sidewards transverse radii was consistent with unity and independent of kT.
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(2002) Physical review letters. 88, 19, p. 6 Abstract[All authors]
Transverse momentum spectra of electrons from [Formula presented] collisions at [Formula presented] have been measured at midrapidity by the PHENIX experiment at the Relativistic Heavy Ion Collider. The spectra show an excess above the background from photon conversions and light hadron decays. The electron signal is consistent with that expected from semileptonic decays of charm. The yield of the electron signal [Formula presented] for [Formula presented] is [Formula presented] in central collisions, and the corresponding charm cross section is [Formula presented] per binary nucleon-nucleon collision.
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(2002) Physical review letters. 88, 19, p. 1923031-1923036 192303. Abstract[All authors]
Transverse momentum spectra of electrons from Au + Au collisions was measured at √sNN = 130 GeV. An excess above the background from light hadron decays and photon conversions was shown by the spectra. The electron signal was found to be consistenent with that expected from semileptonic decay of charm.
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(2002) Physical Review C - Nuclear Physics. 65, 3, p. 319011-319014 031901. Abstract[All authors]
We present results for the charged-particle multiplicity distribution at midrapidity in Au - Au collisions at √sNN = 130 GeV measured with the PHENIX detector at RHIC. For the 5% most central collisions we find dNch/dη|η=0 = 622±1(stat)±41(syst). The results, analyzed as a function of centrality, show a steady rise of the particle density per participating nucleon with centrality.
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Charged particle multiplicity and transverse energy in Au-Au collisions at root(S)(NN)=130 GeV(2002) Nuclear Physics A. 698, p. 171C-176C Abstract
This paper presents the results for the charged-particle multiplicity and transverse energy distributions at mid-rapidity in Au - Au collisions at roots(NN) = 130 GeV measured with the PHENIX detector at RHIC. The values of dN(ch)/deta(\eta=0) and dE(T)/deta(\eta=0), analyzed as a function of centrality, show a consistent steady rise. For the 5% most central collisions they are similar to 70% larger compared to the SPS results for Pb-Pb collisions at roots(NN) = GeV. The ratio of / remains constant as a function of centrality at 0.8 GeV, as also observed at the SPS at CERN and at the AGS at BNL.
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(2002) Physical review letters. 88, 2, 022301. Abstract
Transverse momentum spectra for charged hadrons and for neutral pions in the range 1GeV/c
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(2002) Physical review letters. 88, 2, p. 6 Abstract[All authors]
Transverse momentum spectra for charged hadrons and for neutral pions in the range [Formula presented] have been measured by the PHENIX experiment at RHIC in [Formula presented] collisions at [Formula presented]. At high [Formula presented] the spectra from peripheral nuclear collisions are consistent with scaling the spectra from [Formula presented] collisions by the average number of binary nucleon-nucleon collisions. The spectra from central collisions are significantly suppressed when compared to the binary-scaled [Formula presented] expectation, and also when compared to similarly binary-scaled peripheral collisions, indicating a novel nuclear-medium effect in central nuclear collisions at RHIC energies.
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2001
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(2001) Physical review letters. 87, 5, p. 52301-1-52301-6 Abstract
The first measurement of energy produced transverse to the beam direction at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory is presented. The midrapidity transverse energy density per participating nucleon rises steadily with the number of participants, closely paralleling the rise in charged-particle density, such that ⟨ET⟩/⟨Nch⟩ remains relatively constant as a function of centrality. The energy density calculated via Bjorkens prescription for the 2% most central Au + Au collisions at √sNN = 130GeV is at least εBj = 4.6GeV/fm3, which is a factor of 1.6 larger than found at √sNN = 17.2GeV(Pb + Pb at CERN).
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Measurement of the midrapidity transverse energy distribution from √SNN = 130 Ge V Au + Au collisions at RHIC(2001) Physical review letters. 87, 5, p. 052301/1-052301/6 052301. Abstract[All authors]
The midrapidity transverse energy density for central Au + Au collisions was measured. It was found that such density is at least 1.6 times larger at √SNN=130 GeV (RHIC) than at √SNN = 17.2 GeV (CERN). The variation of the ET density per participant with centrality was observed to be very similar to the previously reported dependence of charged multiplicity density per participant at RHIC energies.
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(2001) Physical review letters. 86, 16, p. 3500-3505 Abstract[All authors]
Using the PHENIX detector, the charged-particle multiplicity distribution at midrapidity in Au-Au collisions at √SNN = 130 GeV was measured. The results of the study are the first RHIC results to span a broad impact parameter range.
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(2001) Pramana - Journal of Physics. 57, 2-3, p. 355-369 Abstract[All authors]
The PHENIX experiment consists of a large detector system located at the newly commissioned relativistic heavy ion collider (RHIC) at the Brookhaven National Laboratory. The primary goal of the PHENIX experiment is to look for signatures of the QCD prediction of a deconfined high-energy-density phase of nuclear matter quark gluon plasma. PHENIX started data taking for Au+Au collisions at √sNN = 130 GeV in June 2000. The signals from the beam-beam counter (BBC) and zero degree calorimeter (ZDC) are used to determine the centrality of the collision. A Glauber model reproduces the ZDC spectrum reasonably well to determine the participants in a collision. Charged particle multiplicity distribution from the first PHENIX paper is compared with the other RHIC experiment and the CERN, SPS results. Transverse momentum of photons are measured in the electro-magnetic calorimeter (EMCal) and preliminary results are presented. Particle identification is made by a time of flight (TOF) detector and the results show clear separation of the charged hadrons from each other.
1999
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(1999) Nuclear Physics A. 661, p. 665C-668C Abstract
A new concept for two-dimensional position readout of wire chambers is described. The basic idea is to use a cathode segmented into small pixels that are read out in specific groups (pads). The electronics is mounted on the outer face of the chamber with a chip-on-board technique, pushing the material thickness to a minimum. The system described here, containing 210 000 readout channels, will be used to read out the pad chambers in the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC).
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