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Register a new userProbe the QCD phase boundary with elliptic flow in relativistic heavy ion collisions at STAR
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Shusu Shi
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We present measurement of elliptic flow, $v_2$, for charged and identified particles at midrapidity in Au+Au collisions at $sqrt{s_{NN}}$ = 7.7 - 39 GeV. We compare the inclusive charged hadron $v_2$ to those from transport model calculations, such as UrQMD model, AMPT default model and AMPT string-melting model. We discuss the energy dependence of the difference in $v_2$ between particles and anti-particles. The $v_2$ of $phi$ meson is observed to be systematically lower than other particles in Au+Au collisions at $sqrt{s_{NN}}$ = 11.5 GeV.
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We present phi-meson transverse momentum distribution as well as its elliptic flow (v_{2}) measurements in Au + Au collisions at center-of-mass energy per nucleon pair sqrt{s_{NN}} = 7.7, 11.5 and 39 GeV with the data taken from STAR experiment at RHIC in the year 2010. We discuss the energy dependence of phi-meson elliptic flow (v_{2}) and central-to-peripheral nuclear modification factors (R_{CP}). The v_{2} of phi-mesons are compared to those from other hadron species. The implications on partonic-hadronic phase transition are discussed.
We study effects of eccentricity fluctuations on the elliptic flow coefficient v_2 at mid-rapidity in both Au+Au and Cu+Cu collisions at sqrt{s_NN}=200 GeV by using a hybrid model that combines ideal hydrodynamics for space-time evolution of the quark gluon plasma phase and a hadronic transport model for the hadronic matter. For initial conditions in hydrodynamic simulations, both the Glauber model and the color glass condensate model are employed to demonstrate the effect of initial eccentricity fluctuations originating from the nucleon position inside a colliding nucleus. The effect of eccentricity fluctuations is modest in semicentral Au+Au collisions, but significantly enhances v_2 in Cu+Cu collisions.
In nucleus-nucleus collisions at ultra-relativistic energies matter is formed with initial energy density significantly exceeding the critical energy density for the transition from hadronic to partonic matter. We will review the experimental evidence for this new form of matter - the Quark-Gluon Plasma - from recent experiments at the SPS and RHIC with emphasis on collective behavior, thermalization, and its opacity for fast partons. We will further show that one can determine from the data a fundamental QCD parameter, the critical temperature for the QCD phase transition.
Elliptic flow (v_2) values for identified particles at midrapidity in Au + Au collisions measured by the STAR experiment in the Beam Energy Scan at the Relativistic Heavy Ion Collider at sqrt{s_{NN}}= 7.7--62.4 GeV are presented for three centrality classes. The centrality dependence and the data at sqrt{s_{NN}}= 14.5 GeV are new. Except at the lowest beam energies we observe a similar relative v_2 baryon-meson splitting for all centrality classes which is in agreement within 15% with the number-of-constituent quark scaling. The larger v_2 for most particles relative to antiparticles, already observed for minimum bias collisions, shows a clear centrality dependence, with the largest difference for the most central collisions. Also, the results are compared with A Multiphase Transport Model and fit with a Blast Wave model.
After decades of painstaking research, the field of heavy ion physics has reached an exciting new era. Evidence is mounting that we can create a high temperature, high density, strongly interacting ``bulk matter state in the laboratory -- perhaps even a quark-gluon plasma. This strongly interacting matter is likely to provide qualitative new information about the fundamental strong interaction, described by Quantum Chromodynamics (QCD). These lectures provide a summary of experimental heavy ion research, with particular emphasis on recent results from RHIC (Relativistic Heavy Ion Collider) at Brookhaven National Laboratory. In addition, we will discuss what has been learned so far and the outstanding puzzles.
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