Correlated fluctuations near the QCD critical point

TL;DR

This paper develops a freeze-out scheme near the QCD critical point, coupling particles with the order parameter field to study correlated fluctuations of net protons, and compares results with STAR experimental data.

Contribution

It introduces a novel freeze-out scheme incorporating static critical fluctuations to model net proton fluctuations near the QCD critical point.

Findings

Model roughly reproduces energy-dependent cumulant $C_4$ and $\kappa \sigma^2$ of net protons.

Calculated $C_2$ and $C_3$ are higher than experimental data due to static critical fluctuations.

Further work needed on dynamical fluctuations and realistic baselines.

Abstract

In this paper, we introduce a freeze-out scheme for the dynamical models near the QCD critical point through coupling the decoupled classical particles with the order parameter field. With a modified distribution function that satisfies specific static fluctuations, we calculate the correlated fluctuations of net protons on the hydrodynamic freeze-out surface. A comparison with recent STAR data shows that our model calculations could roughly reproduce energy dependent cumulant $C_4$ and $\kappa \sigma^2$ of net protons through tuning the related parameters. However, the calculated $C_2$ and $C_3$ with both Poisson and Binomial baselines are always above the experimental data due to the positive contributions from the static critical fluctuations. In order to qualitatively and quantitatively describe the experimental data, the dynamical critical fluctuations and more realistic non-critical fluctuation baselines should be investigated in the near future.