Search for the QCD Critical Point by Higher Moments of Net-proton Multiplicity Distributions at RHIC

TL;DR

This study measures higher moments of net-proton distributions in various heavy-ion collisions at RHIC energies to search for the QCD critical point, finding consistency with models at high energies and deviations at lower energies.

Contribution

It provides the first comprehensive measurement of net-proton higher moments across multiple collision systems and energies, offering insights into the QCD phase diagram and critical point search.

Findings

Moment products align with models at high energies.

Deviations observed at lower energies suggest possible critical phenomena.

Results contribute to understanding QCD matter and phase transitions.

Abstract

Higher moments of net-proton multiplicity distributions are applied to search for the QCD critical point. In this paper, we will present measurements for kurtosis ($\kappa$), skewness ($S$) and variance $\sigma^2$) of net-proton multiplicity distributions at the mid-rapidity ($|y|<0.5$) and transverse momentum range $0.4<p_{T}<0.8$ {\gevc} for Au+Au collisions at {\sNN} = 7.7, 11.5, 39, 62.4 and 200 GeV, Cu+Cu collisions at {\sNN} = 22.4, 62.4 and 200 GeV, $d$+Au collisions at {\sNN} = 200 GeV and p+p collisions at {\sNN} = 62.4 and 200 GeV. The moment products $\kappa \sigma^2$ and $S \sigma$ of net-proton distributions, which are related to volume independent baryon number susceptibility ratios, are consistent with Lattice QCD and Hadron Resonance Gas (HRG) model calculations at high energies ({\sNN} = 62.4 and 200 GeV). Deviations of $\kappa \sigma^2$ and $S\sigma$ for the Au+Au collisions at low energies ({\sNN} = 7.7, 11.5 and 39 GeV) from HRG model calculations are also observed.