Event anisotropy v2 in Au + Au collisions at sNN=7.7–62.4 GeV with STAR

Shusu Shi

doi:10.1016/j.nuclphysa.2013.02.159

Abstract

We present the $v_2$ measurement at midrapidity from Au+Au collisions at $\sqrt{s_{NN}}=$ 7.7, 11.5, 19.6, 27, 39 and 62.4 GeV for inclusive charged hadrons and identified hadrons ($\pi^{\pm}$, $K^{\pm}$, $K_{S}^{0}$, $p$, $\bar{p}$, $\phi$, $\Lambda$, $\bar{\Lambda}$, $\Xi^{-}$, $\bar{\Xi}^{+}$, $\Omega^{-}$, $\bar{\Omega}^{+}$) up to 4 GeV/$c$ in $p_{T}$. The beam energy and centrality dependence of charged hadron $v_2$ are presented with comparison to higher energies at RHIC and LHC. The identified hadron $v_{2}$ are used to discuss the NCQ scaling for different beam energies. Significant difference in $v_{2}(p_{T})$ is observed between particles and corresponding anti-particles for $\sqrt{s_{NN}} <$ 39 GeV. These differences are more pronounced for baryons compared to mesons and they increase with decreasing energy.

Highlights

Searching for the phase boundary in the Quantum ChromoDynamics (QCD) phase diagram is one of the main motivations of the Beam Energy Scan (BES) program at RHIC
For pT below 2 GeV/c, the v2 values rise with increasing collision energy
The increase of v2(pT ) as a function of energy could be due to the change of chemical composition from low to high energies and/or larger collectivity at higher collision energy

Summary

Introduction

Searching for the phase boundary in the Quantum ChromoDynamics (QCD) phase diagram is one of the main motivations of the Beam Energy Scan (BES) program at RHIC. The v2 from other energies are divided by the fit and shown in the lower panels of Fig. 1. For pT below 2 GeV/c, the v2 values rise with increasing collision energy. Beyond pT = 2 GeV/c the v2 results show comparable values within statistical errors.

Results

Conclusion