113 research outputs found

    Electron-muon correlation as a new probe to strongly interacting quark-gluon plasma

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    As a new and clean probe to the strongly interacting quark-gluon plasma (sQGP), we propose an azimuthal correlation of an electron and a muon which originate from the semileptonic decay of charm and bottom quarks. By solving the Langevin equation for the heavy quarks under the hydrodynamic evolution of the hot plasma, we show that substantial quenching of the away-side peak in the electron-muon correlation can be seen if the sQGP drag force acting on heavy quarks is large enough as suggested from the gauge/gravity correspondence. The effect could be detected in high-energy heavy-ion collisions at the Relativistic Heavy Ion Collider and the Large Hadron Collider.Comment: 4 pages, 2 figure

    RHIC physics overview

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    The results from data taken during the last several years at the Relativistic Heavy-Ion Collider (RHIC) will be reviewed in the paper. Several selected topics that further our understanding of constituent quark scaling, jet quenching and color screening effect of heavy quarkonia in the hot dense medium will be presented. Detector upgrades will further probe the properties of Quark Gluon Plasma. Future measurements with upgraded detectors will be presented. The discovery perspectives from future measurements will also be discussed.Comment: 9 pages, 4 figures, invited review article, published by Frontier of Physics in Chin

    An Experimental Exploration of the QCD Phase Diagram: The Search for the Critical Point and the Onset of De-confinement

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    The QCD phase diagram lies at the heart of what the RHIC Physics Program is all about. While RHIC has been operating very successfully at or close to its maximum energy for almost a decade, it has become clear that this collider can also be operated at lower energies down to 5 GeV without extensive upgrades. An exploration of the full region of beam energies available at the RHIC facility is imperative. The STAR detector, due to its large uniform acceptance and excellent particle identification capabilities, is uniquely positioned to carry out this program in depth and detail. The first exploratory beam energy scan (BES) run at RHIC took place in 2010 (Run 10), since several STAR upgrades, most importantly a full barrel Time of Flight detector, are now completed which add new capabilities important for the interesting physics at BES energies. In this document we discuss current proposed measurements, with estimations of the accuracy of the measurements given an assumed event count at each beam energy.Comment: 59 pages, 78 figure

    Measurements of Dihadron Correlations Relative to the Event Plane in Au+Au Collisions at sNN=200\sqrt{s_{NN}}=200 GeV

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    Dihadron azimuthal correlations containing a high transverse momentum (\pt) trigger particle are sensitive to the properties of the nuclear medium created at RHIC through the strong interactions occurring between the traversing parton and the medium, i.e. jet-quenching. Previous measurements revealed a strong modification to dihadron azimuthal correlations in Au+Au collisions with respect to \pp\ and \dAu\ collisions. The modification increases with the collision centrality, suggesting a path-length dependence to the jet-quenching effect. This paper reports STAR measurements of dihadron azimuthal correlations in mid-central (20-60\%) Au+Au collisions at \snn=200~GeV as a function of the trigger particle's azimuthal angle relative to the event plane, \phis=|\phit-\psiEP|. The azimuthal correlation is studied as a function of both the trigger and associated particle \pt. The subtractions of the combinatorial background and anisotropic flow, assuming Zero Yield At Minimum (\zyam), are described. The away-side correlation is strongly modified, and the modification varies with \phis, which is expected to be related to the path-length that the away-side parton traverses. The pseudo-rapidity (\deta) dependence of the near-side correlation, sensitive to long range \deta correlations (the ridge), is also investigated. The ridge and jet-like components of the near-side correlation are studied as a function of \phis. The ridge appears to drop with increasing \phis while the jet-like component remains approximately constant. ...Comment: 50 pages, 39 figures, 6 table

    Growth of Long Range Forward-Backward Multiplicity Correlations with Centrality in Au+Au Collisions at sNN\sqrt{s_{NN}} = 200 GeV

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    Forward-backward multiplicity correlation strengths have been measured with the STAR detector for Au+Au and p+p\textit{p+p} collisions at sNN\sqrt{s_{NN}} = 200 GeV. Strong short and long range correlations (LRC) are seen in central Au+Au collisions. The magnitude of these correlations decrease with decreasing centrality until only short range correlations are observed in peripheral Au+Au collisions. Both the Dual Parton Model (DPM) and the Color Glass Condensate (CGC) predict the existence of the long range correlations. In the DPM the fluctuation in the number of elementary (parton) inelastic collisions produces the LRC. In the CGC longitudinal color flux tubes generate the LRC. The data is in qualitative agreement with the predictions from the DPM and indicates the presence of multiple parton interactions.Comment: 6 pages, 3 figures The abstract has been slightly modifie

    Measurements of ϕ\phi meson production in relativistic heavy-ion collisions at RHIC

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    We present results for the measurement of ϕ\phi meson production via its charged kaon decay channel ϕK+K\phi \to K^+K^- in Au+Au collisions at sNN=62.4\sqrt{s_{_{NN}}}=62.4, 130, and 200 GeV, and in p+pp+p and dd+Au collisions at sNN=200\sqrt{s_{_{NN}}}=200 GeV from the STAR experiment at the BNL Relativistic Heavy Ion Collider (RHIC). The midrapidity (y<0.5|y|<0.5) ϕ\phi meson transverse momentum (pTp_{T}) spectra in central Au+Au collisions are found to be well described by a single exponential distribution. On the other hand, the pTp_{T} spectra from p+pp+p, dd+Au and peripheral Au+Au collisions show power-law tails at intermediate and high pTp_{T} and are described better by Levy distributions. The constant ϕ/K\phi/K^- yield ratio vs beam species, collision centrality and colliding energy is in contradiction with expectations from models having kaon coalescence as the dominant mechanism for ϕ\phi production at RHIC. The Ω/ϕ\Omega/\phi yield ratio as a function of pTp_{T} is consistent with a model based on the recombination of thermal ss quarks up to pT4p_{T}\sim 4 GeV/cc, but disagrees at higher transverse momenta. The measured nuclear modification factor, RdAuR_{dAu}, for the ϕ\phi meson increases above unity at intermediate pTp_{T}, similar to that for pions and protons, while RAAR_{AA} is suppressed due to the energy loss effect in central Au+Au collisions. Number of constituent quark scaling of both RcpR_{cp} and v2v_{2} for the ϕ\phi meson with respect to other hadrons in Au+Au collisions at sNN\sqrt{s_{_{NN}}}=200 GeV at intermediate pTp_{T} is observed. These observations support quark coalescence as being the dominant mechanism of hadronization in the intermediate pTp_{T} region at RHIC.Comment: 22 pages, 21 figures, 4 table

    Charged and strange hadron elliptic flow in Cu+Cu collisions at sNN\sqrt{s_{NN}} = 62.4 and 200 GeV

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    We present the results of an elliptic flow analysis of Cu+Cu collisions recorded with the STAR detector at 62.4 and 200GeV. Elliptic flow as a function of transverse momentum is reported for different collision centralities for charged hadrons and strangeness containing hadrons KS0K_{S}^{0}, Λ\Lambda, Ξ\Xi, ϕ\phi in the midrapidity region eta<1.0|eta|<1.0. Significant reduction in systematic uncertainty of the measurement due to non-flow effects has been achieved by correlating particles at midrapidity, η<1.0|\eta|<1.0, with those at forward rapidity, 2.5<η<4.02.5<|\eta|<4.0. We also present azimuthal correlations in p+p collisions at 200 GeV to help estimating non-flow effects. To study the system-size dependence of elliptic flow, we present a detailed comparison with previously published results from Au+Au collisions at 200 GeV. We observe that v2v_{2}(pTp_{T}) of strange hadrons has similar scaling properties as were first observed in Au+Au collisions, i.e.: (i) at low transverse momenta, pT<2GeV/cp_T<2GeV/c, v2v_{2} scales with transverse kinetic energy, mTmm_{T}-m, and (ii) at intermediate pTp_T, 2<pT<4GeV/c2<p_T<4GeV/c, it scales with the number of constituent quarks, nqn_q. We have found that ideal hydrodynamic calculations fail to reproduce the centrality dependence of v2v_{2}(pTp_{T}) for KS0K_{S}^{0} and Λ\Lambda. Eccentricity scaled v2v_2 values, v2/ϵv_{2}/\epsilon, are larger in more central collisions, suggesting stronger collective flow develops in more central collisions. The comparison with Au+Au collisions which go further in density shows v2/ϵv_{2}/\epsilon depend on the system size, number of participants NpartN_{part}. This indicates that the ideal hydrodynamic limit is not reached in Cu+Cu collisions, presumably because the assumption of thermalization is not attained.Comment: 18 pages, 14 figure

    Studies of di-jet survival and surface emission bias in Au+Au collisions via angular correlations with respect to back-to-back leading hadrons

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    We report first results from an analysis based on a new multi-hadron correlation technique, exploring jet-medium interactions and di-jet surface emission bias at RHIC. Pairs of back-to-back high transverse momentum hadrons are used for triggers to study associated hadron distributions. In contrast with two- and three-particle correlations with a single trigger with similar kinematic selections, the associated hadron distribution of both trigger sides reveals no modification in either relative pseudo-rapidity or relative azimuthal angle from d+Au to central Au+Au collisions. We determine associated hadron yields and spectra as well as production rates for such correlated back-to-back triggers to gain additional insights on medium properties.Comment: By the STAR Collaboration. 6 pages, 2 figure

    System-Size Independence of Directed Flow Measured at the BNL Relativistic Heavy-Ion Collider

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    We measure directed flow (ν_1) for charged particles in Au+Au and Cu+Cu collisions at √S_(NN)=200 and 62.4 GeV, as a function of pseudorapidity (η), transverse momentum (p_t), and collision centrality, based on data from the STAR experiment. We find that the directed flow depends on the incident energy but, contrary to all available model implementations, not on the size of the colliding system at a given centrality. We extend the validity of the limiting fragmentation concept to ν_1 in different collision systems, and investigate possible explanations for the observed sign change in ν_1(p_t)

    Studying Parton Energy Loss in Heavy-Ion Collisions via Direct-Photon and Charged-Particle Azimuthal Correlations

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    Charged-particle spectra associated with direct photon (γdir\gamma_{dir} ) and π0\pi^0 are measured in pp+pp and Au+Au collisions at center-of-mass energy sNN=200\sqrt{s_{_{NN}}}=200 GeV with the STAR detector at RHIC. A hower-shape analysis is used to partially discriminate between γdir\gamma_{dir} and π0\pi^0. Assuming no associated charged particles in the γdir\gamma_{dir} direction (near side) and small contribution from fragmentation photons (γfrag\gamma_{frag}), the associated charged-particle yields opposite to γdir\gamma_{dir} (away side) are extracted. At mid-rapidity (η<0.9|\eta|<0.9) in central Au+Au collisions, charged-particle yields associated with γdir\gamma_{dir} and π0\pi^0 at high transverse momentum (8<pTtrig<168< p_{T}^{trig}<16 GeV/cc) are suppressed by a factor of 3-5 compared with pp + pp collisions. The observed suppression of the associated charged particles, in the kinematic range η<1|\eta|<1 and 3<pTassoc<163< p_{T}^{assoc} < 16 GeV/cc, is similar for γdir\gamma_{dir} and π0\pi^0, and independent of the γdir\gamma_{dir} energy within uncertainties. These measurements indicate that the parton energy loss, in the covered kinematic range, is insensitive to the parton path length.Comment: submitted to Phys. Rev. Lett, 6 pages, 4 figure
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