Contrasting Freezeouts in Large Versus Small Systems

TL;DR

This paper compares different chemical freezeout models in small and large collision systems at the LHC, revealing a system size dependence in the preferred freezeout scheme based on hadron yield data.

Contribution

It introduces a comparative analysis of freezeout schemes in different collision systems, highlighting the system size influence on the freezeout process.

Findings

p+p and p+Pb favor 1CFO+γ_S scheme with γ_S approaching 1

Mid-central to central Pb+Pb favor 2CFO scheme

Freezeout scheme dependence suggests additional interactions in larger systems

Abstract

We study the data on mean hadron yields and contrast the chemical freezeout conditions in p+p, p+Pb and Pb+Pb at the Large Hadron Collider (LHC) energies. We study several schemes for freezeout that mainly differ in the way strangeness is treated: i. strangeness freezes out along with the non-strange hadrons in complete equilibrium (1CFO), ii. strangeness freezes out along with non-strange hadrons with an additional parameter $\gamma_S$ accounting for non-equilibrium production of strangeness (1CFO+$\gamma_S$), and iii. strangeness freezes out earlier than non-strange hadrons and in thermal equilibrium (2CFO). A comparison of the chisquares of the fits indicate a dependence of the freezeout scheme on the system size. The minimum bias p+p and different centralities of p+Pb and peripheral Pb+Pb data prefer 1CFO$+\gamma_S$ with $\gamma_S$ approaching unity as we go from p+p to central p+Pb and peripheral Pb+Pb. On the other hand, the mid-central to central Pb+Pb data prefer 2CFO over 1CFO+$\gamma_S$. Such system size dependence of freezeout scheme could be an indication of the additional interaction in Pb+Pb over p+Pb and p+p.