Centrality dependence of chemical freeze-out parameters from net-proton and net-charge fluctuations using hadron resonance gas model

TL;DR

This study estimates chemical freeze-out parameters in heavy-ion collisions using the HRG model, revealing energy and centrality dependencies, and scaling behaviors in fluctuation measurements across different collision energies.

Contribution

It introduces a detailed analysis of freeze-out parameters from net-proton and net-charge fluctuations, highlighting deviations at lower energies and centralities, and explores scaling behaviors in these parameters.

Findings

Freeze-out parameters are similar at high energies but deviate at lower energies.

Scaling behavior observed for lower order fluctuations, violated at certain energies.

Different fluctuation measures (σ²/M and sσ) are described by different freeze-out parameters.

Abstract

We estimate chemical freeze-out parameters in HRG and EVHRG model by fitting the experimental information of net-proton and net-charge fluctuations measured in Au + Au collisions by the STAR collaboration at RHIC. We observe that chemical freeze-out parameters obtained from lower and higher order fluctuations are though almost same for $\sqrt{s_{NN}} > 27$ GeV, tend to deviate from each other at lower $\sqrt{s_{NN}}$. Moreover, these separations increase with decrease of $\sqrt{s_{NN}}$ and for a fixed $\sqrt{s_{NN}}$ increase towards central collisions. Furthermore, we observe an approximate scaling behaviour of $(\mu_B/T)/(\mu_B/T)_{central}$ with $(N_{part})/(N_{part})_{central}$ for the parameters estimated from lower order fluctuations for 11.5 GeV $\le \sqrt{s_{NN}} \le$ 200 GeV. Scaling is violated for the parameters estimated from higher order fluctuations for $\sqrt{s_{NN}}= 11.5$ and 19.6 GeV. It is observed that the chemical freeze-out parameter, which can describe $\sigma^2/M$ of net-proton very well in all energies and centralities, can not describe the $s\sigma$ equally well and vice versa.