Spectra and radial flow at RHIC with Tsallis statistics in a Blast-Wave description

TL;DR

This study introduces a Tsallis statistics-based Blast-Wave model to analyze RHIC particle spectra, revealing a transition from non-equilibrium in p+p to thermalization in central Au+Au collisions, with distinct parameter sets needed for different collision types.

Contribution

The paper develops and applies a Tsallis Blast-Wave model to RHIC data, providing new insights into the system's thermalization and flow properties across collision systems.

Findings

Flow velocity increases from zero in p+p to 0.470c in central Au+Au.

The non-equilibrium parameter (q-1) decreases from 0.100 to 0.015.

Different parameter sets are needed for mesons and baryons in p+p, but not in Au+Au.

Abstract

We have implemented the Tsallis statistics in a Blast-Wave model and applied it to mid-rapidity transverse-momentum spectra of identified particles measured at RHIC. This new Tsallis Blast-Wave function fits the RHIC data very well for $p_T<$3 GeV/$c$. We observed that the collective flow velocity starts from zero in p+p and peripheral Au+Au collisions growing to 0.470 $\pm$ 0.009($c$) in central Au+Au collisions. The $(q-1)$ parameter, which characterizes the degree of non-equilibrium in a system, changes from $0.100\pm0.003$ in p+p to $0.015\pm0.005$ in central Au+Au collisions, indicating an evolution from a highly non-equilibrated system in p+p collisions toward an almost thermalized system in central Au+Au collisions. The temperature and collective velocity are well described by a quadratic dependence on $(q-1)$. Two sets of parameters in our Tsallis Blast-Wave model are required to describe the meson and baryon groups separately in p+p collisions while one set of parameters appears to fit all spectra in central Au+Au collisions.