Quantifying fluctuation signatures of the QCD critical point using maximum entropy freeze-out

TL;DR

This paper develops a theoretical framework using maximum entropy methods to analyze fluctuations in proton multiplicities in heavy-ion collisions, aiming to identify signatures of the QCD critical point.

Contribution

It introduces a maximum entropy approach to connect QCD thermodynamics with experimental particle fluctuation data near a critical point.

Findings

Quantifies the impact of non-universal parameters on factorial cumulants.

Provides estimates for proton multiplicity fluctuations assuming thermal equilibrium.

Analyzes how the proximity of the critical point affects fluctuation signatures.

Abstract

A key question about the QCD phase diagram is whether there is a critical point somewhere on the boundary between the hadronic and quark-gluon plasma phases, and if so where. Heavy-ion collisions offer a unique opportunity to search for signatures of such a critical point by analyzing event-by-event fluctuations in particle multiplicities. To draw meaningful conclusions from experimental data, a theoretical framework is needed to link QCD thermodynamics with the particle spectra and correlations observed in detectors. The Equation of State (EoS) of QCD near a critical point can be related to the universal Gibbs free energy of the 3D Ising model using four currently unknown non-universal mapping parameters whose values are determined by the microscopic details of QCD. We utilize the maximum entropy approach to freeze-out the fluctuations in order to make estimates for factorial cumulants of proton multiplicities, assuming thermal equilibrium, for a family of EoS with a 3D Ising-like critical point, varying the microscopic inputs that determine the strength and structure of the critical features. We quantify the effect of the non-universal mapping parameters, and the distance between the critical point and the freeze-out curve, on the factorial cumulants of proton multiplicities.