Energy Dependence of High Moments for Net-proton Distributions

TL;DR

This paper investigates how high moments of net-proton distributions behave in heavy-ion collisions using various models, aiming to identify signals of the QCD critical point amid non-critical backgrounds.

Contribution

It demonstrates that non-critical physics backgrounds can mimic critical signals, emphasizing the need for careful interpretation of moment measurements in QCD phase transition studies.

Findings

Moments of net-proton distributions can be described by superposition of emission sources.

Certain moment products remain constant without critical phenomena.

Non-monotonic behavior of moments may indicate the QCD critical point.

Abstract

High moments of multiplicity distributions of conserved quantities are predicted to be sensitive to critical fluctuations. To understand the effect of the complicated non-critical physics backgrounds on the proposed observable, we have studied various moments of net-proton distributions with AMPT, Hijing, Therminator and UrQMD models, in which no QCD critical point physics is implemented. It is found that the centrality evolution of various moments of net-proton distributions can be uniformly described by a superposition of emission sources. In addition, in the absence of critical phenomena, some moment products of net-proton distribution, related to the baryon number susceptibilities ratio in Lattice QCD calculation, are predicted to be constant as a function of the collision centrality. We argue that a non-monotonic dependence of the moment products as a function collision centrality and the beam energy may be used to locate the QCD critical point.