System Size and Flavour Dependence of Chemical Freeze-out Temperatures in ALICE Data from pp, pPb and PbPb Collisions at LHC Energies

TL;DR

This study investigates how chemical freeze-out temperatures vary with system size and particle flavor in high-energy collisions, revealing flavor-dependent effects that explain strangeness enhancement without non-equilibrium assumptions.

Contribution

It introduces a flavor-dependent two-temperature freeze-out model within a canonical ensemble to explain strangeness enhancement across different system sizes at LHC energies.

Findings

Flavor dependence of $T_{ch}$ explains strangeness enhancement.

Two-temperature model fits experimental yields well.

Strangeness canonical ensemble accounts for system size effects.

Abstract

We present the system size and flavour dependence of the chemical freeze-out temperature ($T_\mathrm{ch}$) at vanishing baryo-chemical potential calculated via thermal fits to experimental yields for several multiplicity classes in pp, pPb and PbPb collisions measured by ALICE. Using the Thermal-FIST Hadron Resonance Gas model package, we compare the quality of fits across various treatments of strangeness conservation under different freeze-out conditions as a function of the charged particle multiplicity density $\big \langle dN_\mathrm{ch}/d\eta \big \rangle$. Additionally, we examine how the anti-hadron to pion yield ratios of light and strange baryons, as well as the $\phi$ meson, evolve within a flavour-dependent model. Through a unique two-temperature chemical freeze-out approach, we show that flavour dependence of $T_\mathrm{ch}$ in a Strangeness Canonical Ensemble leads to a natural explanation of strangeness enhancement from small to large systems at LHC energies without requiring any non-equilibrium particle production at small $\big \langle dN_\mathrm{ch}/d\eta \big \rangle$.