43 research outputs found

    Observation of D0D^0 meson nuclear modifications in Au+Au collisions at sNN\sqrt{s_{_{\mathrm{NN}}}} = 200 GeV

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    7 pages including author list, 4 figures ; see paper for full list of authorsWe report the first measurement of charmed-hadron (D0D^0) production via the hadronic decay channel (D0K+π+D^0\rightarrow K^- + \pi^+) in Au+Au collisions at sNN\sqrt{s_{_{\mathrm{NN}}}} = 200\,GeV with the STAR experiment. The charm production cross-section per nucleon-nucleon collision at mid-rapidity scales with the number of binary collisions, NbinN_{bin}, from pp+pp to central Au+Au collisions. The D0D^0 meson yields in central Au+Au collisions are strongly suppressed compared to those in pp+pp scaled by NbinN_{bin}, for transverse momenta p_{T}>3 GeV/cc, demonstrating significant energy loss of charm quarks in the hot and dense medium. An enhancement at intermediate pTp_{T} is also observed. Model calculations including strong charm-medium interactions and coalescence hadronization describe our measurements

    Jet-Hadron Correlations in root s(NN)=200 GeV p plus p and Central Au plus Au Collisions

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    Azimuthal angular correlations of charged hadrons with respect to the axis of a reconstructed (trigger) jet in Au + Au and p + p collisions at root s(NN) = 200 GeV in STAR are presented. The trigger jet population in Au + Au collisions is biased toward jets that have not interacted with the medium, allowing easier matching of jet energies between Au + Au and p + p collisions while enhancing medium effects on the recoil jet. The associated hadron yield of the recoil jet is significantly suppressed at high transverse momentum (p(T)(assoc)) and enhanced at low p(T)(assoc) in 0%-20% central Au + Au collisions compared to p + p collisions, which is indicative of medium-induced parton energy loss in ultrarelativistic heavy-ion collisions

    Elliptic flow of identified hadrons in Au + Au collisions at root s(NN)=7.7-62.4 GeV

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    J/psi polarization in p plus p collisions at root s=200 GeV in STAR

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    We report on a polarization measurement of inclusive J/psi mesons in the di-electron decay channel at mid-rapidity at 2 < p(T) < 6 GeV/c in p + p collisions at root s = 200 GeV. Data were taken with the STAR detector at RHIC. The J/psi polarization measurement should help to distinguish between different models of the J/psi production mechanism since they predict different p(T) dependences of the J/psi polarization. In this analysis, J/psi is studied in the helicity frame. The polarization parameter lambda(theta) measured at RHIC becomes smaller towards high p(T), indicating more longitudinal J/psi polarization as p(T) increases. The result is compared with predictions of presently available models. (C) 2014 The Authors. Published by Elsevier B.V

    Measurement of Longitudinal Spin Asymmetries for Weak Boson Production in Polarized Proton-Proton Collisions at RHIC

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    We report measurements of single- and double-spin asymmetries for W-+/- and Z/gamma* boson production in longitudinally polarized p + p collisions at root s = 510 GeV by the STAR experiment at RHIC. The asymmetries for W-+/- were measured as a function of the decay lepton pseudorapidity, which provides a theoretically clean probe of the proton's polarized quark distributions at the scale of the W mass. The results are compared to theoretical predictions, constrained by polarized deep inelastic scattering measurements, and show a preference for a sizable, positive up antiquark polarization in the range 0.05 < x < 0.2

    Freeze-out dynamics via charged kaon femtoscopy in root sNN=200 GeV central Au plus Au collisions

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    Energy Dependence of Moments of Net-Proton Multiplicity Distributions at RHIC

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    We report the beam energy (root S-NN = 7.7-200 GeV) and collision centrality dependence of the mean (M), standard deviation (sigma), skewness (S), and kurtosis (kappa) of the net-proton multiplicity distributions in Au + Au collisions. The measurements are carried out by the STAR experiment at midrapidity (vertical bar y vertical bar < 0.5) and within the transverse momentum range 0.4 < p(T) < 0.8 GeV/c in the first phase of the Beam Energy Scan program at the Relativistic Heavy Ion Collider. These measurements are important for understanding the quantum chromodynamic phase diagram. The products of the moments, S sigma and K sigma(2), are sensitive to the correlation length of the hot and dense medium created in the collisions and are related to the ratios of baryon number susceptibilities of corresponding orders. The products of moments are found to have values significantly below the Skellam expectation and close to expectations based on independent proton and antiproton production. The measurements are compared to a transport model calculation to understand the effect of acceptance and baryon number conservation and also to a hadron resonance gas model

    Observation of an Energy-Dependent Difference in Elliptic Flow between Particles and Antiparticles in Relativistic Heavy Ion Collisions

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    System-size dependence of transverse momentum correlations at root s(NN)=62.4 and 200 GeV at the BNL Relativistic Heavy Ion Collider

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    Measurement of J/psi Azimuthal Anisotropy in Au plus Au Collisions at root s(NN)=200 GeV

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