Dynamical net-proton fluctuations near a QCD critical point

TL;DR

This paper studies how net-proton and chiral order parameter fluctuations evolve near a QCD critical point in heavy-ion collisions, highlighting the impact of nonequilibrium dynamics on critical signals.

Contribution

It introduces a dynamical model coupling chiral order parameter evolution with an expanding quark-gluon fluid to analyze fluctuation signals near the QCD critical point.

Findings

Critical fluctuations produce distinct kurtosis signals compared to initial fluctuations.

Nonequilibrium effects influence the development of critical fluctuation signals.

Critical signals in net-proton kurtosis remain observable despite dynamical effects.

Abstract

We investigate the evolution of the net-proton kurtosis and the kurtosis of the chiral order parameter near the critical point in the model of nonequilibrium chiral fluid dynamics. The order parameter is propagated explicitly and coupled to an expanding fluid of quarks and gluons in order to describe the dynamical situation in a heavy-ion collision. We study the critical region near the critical point on the crossover side. There are two sources of fluctuations: non-critical initial event-by-event fluctuations and critical fluctuations. These fluctuations can be distinguished by comparing a mean-field evolution of averaged thermodynamic quantities with the inclusion of fluctuations at the phase transition. We find that while the initial state fluctuations give rise to flat deviations from statistical fluctuations, critical fluctuations reveal a clear structure of the phase transition. The signals of the critical point in the net-proton and sigma field kurtosis are affected by the nonequilibrium dynamics and the inhomogeneity of the space-time evolution but develop clearly.