Centrality dependence of freeze-out parameters from the beam energy scan at STAR

Abstract

The STAR experiment at RHIC has a unique capability of measuring identified hadrons over a wide range of pseudorapidity ($\eta$), transverse momentum ($p_{T}$), and azimuthal angle ($\phi$) acceptance. The data collected ($\sqrt{s_{NN}}$ = 7.7, 11.5, and 39 GeV) in its beam energy scan (BES) program provide a chance to investigate the final hadronic state freeze-out conditions of ultrarelativistic Au+Au collisions. The particle ratios are used to compare to a statistical model calculation using both grand canonical and strangeness canonical ensembles to extract the chemical freeze-out parameters. The $p_{T}$ distributions are fitted to calculations using a blast-wave model to obtain the kinetic freeze-out parameters. We discuss the centrality dependence of the extracted chemical and kinetic freeze-out parameters at these lower energies.