Role of system size on freezeout conditions extracted from transverse momentum spectra of hadrons

TL;DR

This study analyzes how system size affects freezeout conditions in p+Pb collisions at 5.02 TeV by comparing different freezeout schemes using transverse momentum spectra of hadrons.

Contribution

It introduces a comparative analysis of freezeout schemes in small collision systems, highlighting the preference for a unified freezeout with strangeness non-equilibrium in p+Pb collisions.

Findings

Unified freezeout with strangeness non-equilibrium fits p+Pb data better than separate freezeout schemes.

System size influences the preferred freezeout scheme, with smaller systems favoring unified models.

Results support the idea that smaller systems have less constituent interaction, affecting freezeout conditions.

Abstract

The data on hadron transverse momentum spectra in different centrality classes of p+Pb collisions at $\sqrt{s}_{NN} = 5.02$ TeV has been analysed to extract the freezeout hypersurface within a simultaneous chemical and kinetic freezeout scenario. The freezeout hypersurface has been extracted for three different freezeout schemes that differ in the way strangeness is treated: i. unified freezeout for all hadrons in complete thermal equilibrium (1FO), ii. unified freezeout for all hadrons with an additional parameter $\gamma_S$ which accounts for possible out-of-equilibrium production of strangeness (1FO$+\gamma_S$), and iii. separate freezeout for hadrons with and without strangeness content (2FO). Unlike in heavy ion collisions where 2FO performs best in describing the mean hadron yields as well as the transverse momentum spectra, in p+Pb we find that 1FO$+\gamma_S$ with one less parameter than 2FO performs better. This confirms expectations from previous analysis on the system size dependence in the freezeout scheme with mean hadron yields: while heavy ion collisions that are dominated by constituent interactions prefer 2FO, smaller collision systems like proton + nucleus and proton + proton collisions with lesser constituent interaction prefer a unified freezeout scheme with varying degree of strangeness equilibration.