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

TL;DR

This paper investigates how the chemical and kinetic freeze-out parameters in gold-gold collisions vary with collision centrality at different energies, using particle ratios and transverse momentum distributions from the STAR experiment.

Contribution

It provides the first detailed analysis of the centrality dependence of freeze-out parameters at lower beam energies in the RHIC BES program.

Findings

Freeze-out parameters vary with collision centrality.

Chemical freeze-out temperature shows a specific dependence on centrality.

Kinetic freeze-out conditions are extracted using blast-wave fits.

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.