Hyper-order baryon number fluctuations at finite temperature and density

TL;DR

This study calculates high-order baryon number fluctuations at finite temperature and density using a QCD-inspired effective theory, revealing potential signatures of the QCD critical point in heavy-ion collision experiments.

Contribution

It provides the first direct computation of tenth-order baryon fluctuations at finite density within a QCD-assisted effective framework, assessing the applicability of low-density expansions.

Findings

Non-monotonic energy dependence of fluctuations observed

Results align with STAR experimental data

Indicates possible signals of a QCD critical point

Abstract

Fluctuations of conserved charges are sensitive to the QCD phase transition and a possible critical endpoint in the phase diagram at finite density. In this work, we compute the baryon number fluctuations up to tenth order at finite temperature and density. This is done in a QCD-assisted effective theory that accurately captures the quantum- and in-medium effects of QCD at low energies. A direct computation at finite density allows us to assess the applicability of expansions around vanishing density. By using different freeze-out scenarios in heavy-ion collisions, we translate these results into baryon number fluctuations as a function of collision energy. We show that a non-monotonic energy dependence of baryon number fluctuations can arise in the non-critical crossover region of the phase diagram. Our results compare well with recent experimental measurements of the kurtosis and the sixth-order cumulant of the net-proton distribution from the STAR collaboration. They indicate that the experimentally observed non-monotonic energy dependence of fourth-order net-proton fluctuations is highly non-trivial. It could be an experimental signature of an increasingly sharp chiral crossover and may indicate a QCD critical point. The physics implications and necessary upgrades of our analysis are discussed in detail.