Critical point of nuclear matter and beam energy dependence of net proton number fluctuations

TL;DR

This study investigates how net proton fluctuations vary with collision energy, revealing potential signals of the nuclear liquid-gas critical point through deviations in skewness and kurtosis, influenced by baryon interactions.

Contribution

It introduces a hadron resonance gas model with van der Waals interactions to analyze net baryon fluctuations and identifies unique energy-dependent signatures of the nuclear critical point.

Findings

Non-monotonic energy dependence of kurtosis $\

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Significant differences between net proton and net baryon fluctuations when baryon interactions are considered.

Abstract

The beam energy dependence of net baryon number susceptibilities is studied in the framework of the hadron resonance gas model with the attractive and repulsive van der Waals interactions between baryons. The collision energy dependences for the skewness $S\sigma$ and kurtosis $\kappa\sigma^2$ deviate significantly from the Poisson baseline and demonstrate the existence of rich structures at moderate collision energies. This behavior may result from the critical end point of the nuclear liquid-gas first order phase transition. In particular, $\kappa\sigma^2$ shows a non-monotonic energy dependence, and, in contrast to the standard scenario for the QCD critical point, it does not decrease at low collision energies. It is also found that the measurable net proton fluctuations differ significantly from the net baryon fluctuations when interactions between baryons cannot be neglected. The results are compared with the experimental net proton number fluctuations measured by the STAR collaboration.