Thermodynamic Analysis of Transverse Momentum Spectra in Pb-Pb Collisions at 2.76 TeV: Centrality Dependence of Temperature, Freezeout Parameters and Non-Extensitivity

TL;DR

This paper analyzes transverse momentum spectra in Pb-Pb collisions at 2.76 TeV, revealing how freezeout parameters and non-extensitivity vary with collision centrality and multiplicity, using Tsallis distribution fits.

Contribution

It introduces a detailed thermodynamic analysis of hadron spectra with the Tsallis distribution, highlighting mass-dependent freezeout scenarios and comparing results across different collision energies.

Findings

Parameters increase with centrality and multiplicity, except q.

Mass dependence supports volume differential and multiple freezeout.

Comparison of parameters across LHC and RHIC energies.

Abstract

We study properties of Pb-Pb collisions at 2.76 TeV in mid-rapidity, $|y|<0.5$, based on data by the ALICE Collaboration. In particular, we examine the transverse momentum ($p_T$) spectra of positively charged (identified) hadrons, $\pi^+$, $K^+$ and $p$, generated in various centrality intervals. We perform individual fits using the thermodynamically consistent Tsallis distribution to extract the following quantities: the non-extensitivity parameter, $q$, the effective temperature, $T_{\rm eff}$, the kinetic freezeout volume, $V$, the mean transverse flow velocity, $\beta_T$, the mean kinetic freezeout temperature, $\langle T_0\rangle$, the thermal temperature, $T_{\rm th}$, and the parameter $\zeta$, which characterizes the fluctuating number of generated particles. From peripheral to central collision, and from lower to higher charged particle multiplicity per pseudorapidity unit, $\langle dN_{\rm ch}/d\eta \rangle$, all these quantities are observed to increase, with the exception of $q$, which has the opposite behavior. The parameters $T_{\rm eff}$, $q$, and $V$ depend on the hadron mass in a way that supports the scenarios of volume differential freezeout and multiple kinetic freezeout. Furthermore, we extracted $\langle T_{\rm eff}\rangle$ and $\langle q\rangle$ for different collisions and energies at LHC and RHIC, and compare their dependencies on $\langle dN_{\rm ch}/d\eta \rangle$ and $\langle N_{\rm part} \rangle$.