System size and flavour dependence of chemical freeze-out temperatures in ALICE data from pp, pPb and PbPb collisions at LHC energies

Abstract

We present the system size and flavour dependence of the chemical freeze-out temperature (Tch) 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 〈dNch/dη〉. Additionally, we examine how the anti-hadron to pion yield ratios of light and strange baryons, as well as the ϕ meson, evolve within a flavour-dependent model. Through a unique two-temperature chemical freeze-out approach, we show that flavour dependence of Tch 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 〈dNch/dη〉.

Keywords

• Strangeness enhancement
• Sequential flavour freeze-out
• Statistical hadronization
• Hadron resonance gas