Chemical freeze-out conditions from net-kaon fluctuations at RHIC

TL;DR

This study compares net-kaon fluctuation data from RHIC with a hadron resonance gas model, revealing that strange mesons freeze out at higher temperatures than light hadrons, challenging existing freeze-out parameter assumptions.

Contribution

It demonstrates that current freeze-out parameters cannot reproduce net-kaon fluctuation data, suggesting different freeze-out temperatures for strange and light hadrons.

Findings

Strange mesons freeze out 10-15 MeV higher than light hadrons.

Net-kaon fluctuations are incompatible with existing freeze-out parameters.

Lambda fluctuation measurements are sensitive to freeze-out temperature differences.

Abstract

We compare the mean-over-variance ratio of the net-kaon distribution calculated within a state-of-the-art hadron resonance gas model to the latest experimental data from the Beam Energy Scan at RHIC by the STAR collaboration. Our analysis indicates that it is not possible to reproduce the experimental results using the freeze-out parameters from the existing combined fit of net-proton and net-electric charge mean-over-variance. The strange mesons need about 10-15 MeV higher temperatures than the light hadrons at the highest collision energies. In view of the recent lambda fluctuation measurements, we predict the net-lambda variance-over-mean at the light and strange chemical freeze-out parameters. We observe that the lambda fluctuations are sensitive to the difference in the freeze-out temperatures established in this analysis. Our results have implications for other phenomenological models in the field of relativistic heavy-ion collisions.