Conserved charge fluctuations with HISQ fermions

TL;DR

This paper uses lattice QCD with HISQ fermions to calculate fluctuations of conserved charges, proposing a model-independent method to determine freeze-out parameters in heavy ion collisions from experimental data.

Contribution

It introduces a novel, model-independent approach to extract freeze-out temperature and chemical potential using lattice QCD calculations of charge fluctuations and experimental measurements.

Findings

Calculated cumulants of conserved charge fluctuations at near-physical quark masses.

Proposed a method to determine freeze-out parameters from charge fluctuation ratios.

Demonstrated the feasibility of using lattice results to interpret heavy ion collision data.

Abstract

We calculate cumulants of fluctuations of net-baryon number, net-electric charge and net-strangeness, in the framework of lattice regularized QCD. We use a highly improved staggered quark (HISQ) action on lattices with temporal extent of N_tau=6,8 and 12 and almost physical quark masses. By means of a Taylor expansion in various chemical potentials and under demanding both strangeness neutrality as well as the correct isospin asymmetry, we evaluate these fluctuations at conditions met in heavy ion collisions. Cumulants of net-electric charge fluctuations can, in principle, also be measured in heavy ion experiments. We therefore propose a method to extract freeze-out parameters, such as the freeze-out temperature and baryon chemical potential, based on a comparison of lattice results and experimental measurements of two different ratios of net-electric charge cumulants. As this method involves only (lattice) QCD results and experimental measurements it is model independent and, for the purpose of extracting freeze-out parameters, does not require any input from hadron resonance gas model calculations.