Net Baryon Fluctuations from a Crossover Equation of State

TL;DR

This paper develops a crossover equation of state connecting hadron gas and quark-gluon plasma, accurately matching lattice results and explaining baryon fluctuation measurements in heavy-ion collisions.

Contribution

It introduces a new crossover equation of state that aligns with lattice QCD data and explains experimental baryon fluctuation results in heavy-ion collisions.

Findings

The equation of state matches lattice calculations at various chemical potentials.

It reproduces proton fluctuation data from STAR collaboration.

Fluctuations freeze out at temperatures below chemical freeze-out.

Abstract

We have constructed an equation of state which smoothly interpolates between an excluded volume hadron resonance gas at low energy density to a plasma of quarks and gluons at high energy density. This crossover equation of state agrees very well with lattice calculations at both zero and nonzero baryon chemical potential. We use it to compute the variance, skewness, and kurtosis of fluctuations of baryon number, and compare to measurements of proton number fluctuations in central Au-Au collisions as measured by the STAR collaboration in a beam energy scan at the Relativistic Heavy Ion Collider. The crossover equation of state can reproduce the data if the fluctuations are frozen out at temperatures well below than the average chemical freeze-out.