Freeze-out temperature from net-Kaon fluctuations at RHIC

TL;DR

This study compares net-kaon fluctuation data from RHIC to a hadron resonance gas model, revealing that strange mesons freeze out at higher temperatures than light hadrons, impacting the understanding of chemical freeze-out conditions.

Contribution

It demonstrates that strange mesons require higher freeze-out temperatures than light hadrons, challenging existing combined fit parameters and providing predictions for future Lambda fluctuation measurements.

Findings

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

Net-kaon fluctuations cannot be reproduced with current combined freeze-out parameters.

Lambda fluctuations are sensitive to differences in freeze-out temperatures.

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 future $\Lambda$ fluctuation measurements, we predict the $\Lambda$ variance-over-mean and skewness-times-variance 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.