Freeze-out Conditions in Heavy Ion Collisions from QCD Thermodynamics

TL;DR

This paper uses lattice QCD calculations of charge fluctuation ratios to determine the chemical freeze-out conditions, such as temperature and chemical potentials, in heavy ion collisions, providing a bridge between theory and experimental data.

Contribution

It introduces a method to extract freeze-out parameters from lattice QCD calculations of cumulant ratios, improving the understanding of heavy ion collision thermodynamics.

Findings

Good agreement between hadron resonance gas model and QCD calculations at 150-170 MeV.

Lattice QCD ratios match experimental data, enabling extraction of freeze-out temperature and baryon chemical potential.

Method provides a reliable way to connect QCD thermodynamics with heavy ion collision experiments.

Abstract

We present a determination of chemical freeze-out conditions in heavy ion collisions based on ratios of cumulants of net electric charge fluctuations. These ratios can reliably be calculated in lattice QCD for a wide range of chemical potential values by using a next-to-leading order Taylor series expansion around the limit of vanishing baryon, electric charge and strangeness chemical potentials. From a computation of up to fourth order cumulants and charge correlations we first determine the strangeness and electric charge chemical potentials that characterize freeze-out conditions in a heavy ion collision and confirm that in the temperature range 150 MeV < T < 170 MeV the hadron resonance gas model provides good approximations for these parameters that agree with QCD calculations on the (5-15)% level. We then show that a comparison of lattice QCD results for ratios of up to third order cumulants of electric charge fluctuations with experimental results allows to extract the freeze-out baryon chemical potential and the freeze-out temperature.