Searching for the QCD Critical Point Using Particle Ratio Fluctuations and Higher Moments of Multiplicity Distributions

TL;DR

This paper reports on measurements of particle ratio fluctuations and higher moments of multiplicity distributions in heavy-ion collisions to search for the QCD critical point, finding energy-independent $K/\pi$ fluctuations and increasing $p/\pi$, $K/p$ fluctuations.

Contribution

It provides new experimental data on dynamical fluctuations across various energies, extending the search for the QCD critical point with comprehensive analysis and comparison to theoretical models.

Findings

$K/\pi$ fluctuations are energy-independent.

$p/\pi$ and $K/p$ fluctuations are negative and approach zero at higher energies.

Higher moments of net-proton and net-charge distributions are analyzed for critical point sensitivity.

Abstract

Dynamical fluctuations in global conserved quantities such as baryon number, strangeness, or charge may be observed near a QCD critical point. Results from new measurements of dynamical $K/\pi$, $p/\pi$, and $K/p$ ratio fluctuations are presented. The commencing of a QCD critical point search at RHIC has extended the reach of possible measurements of dynamical $K/\pi$, $p/\pi$, and $K/p$ ratio fluctuations from Au+Au collisions to lower energies. The STAR experiment has performed a comprehensive study of the energy dependence of these dynamical fluctuations in Au+Au collisions at the energies $\sqrt{s_{NN}}$ = 7.7, 11.5, 39, 62.4, and 200 GeV. New results are compared to previous measurements and to theoretical predictions from several models. The measured dynamical $K/\pi$ fluctuations are found to be independent of collision energy, while dynamical $p/\pi$ and $K/p$ fluctuations have a negative value that increases toward zero at top RHIC energy. Fluctuations of the higher moments of conserved quantities (net-proton and net-charge) distributions, which are predicted to be sensitive to the presence of a critical point, are also presented.