Higher Moments of Net-Particle Multiplicity Distributions

TL;DR

This paper reports experimental measurements of higher moments of net-particle multiplicity distributions in high-energy nuclear collisions, providing insights into the phase structure of nuclear matter and completing the first RHIC Beam Energy Scan program.

Contribution

It presents the first experimental results of volume and temperature independent cumulant ratios of net-charge and net-proton distributions across a wide energy range, including the first fully corrected net-kaon results.

Findings

Cumulant ratios of net-charge and net-proton distributions measured at various energies.

First measurement of fully corrected net-kaon cumulant ratios.

Discussion of pseudo-rapidity dependence at 14.5 GeV.

Abstract

Studying fluctuations of conserved quantities, such as baryon number, strangeness, and charge, provides insights into the properties of matter created in high-energy nuclear collisions. Lattice QCD calculations suggest that higher moments of these quantities are sensitive to the phase structure of the hot and dense nuclear matter created in such collisions. In this paper, we present first experimental results of volume and temperature independent cumulant ratios of net-charge and net-proton distributions in Au+Au collisions at $\sqrt{s_{\rm NN}}\!=\!14.5 \,{\rm GeV}$ completing the first RHIC Beam Energy Scan (BES-I) program for $\sqrt{s_{\rm NN}}\!=\!7.7 \,{\rm to}\,200\,{\rm GeV}$, together with the first measurement of fully corrected net-kaon results, measured with the STAR detector at RHIC at mid-rapidity and a transverse momentum up to $p_{\rm T}\!=\!2\,{\rm GeV/{\it c}}$. The pseudo-rapidity dependence of the $\sqrt{s_{\rm NN}}\!=\!14.5 \,{\rm GeV}$ net-charge cumulant ratios is discussed. The estimated uncertainties on the ratio $c_4/c_2$, the most statistics-hungry of the present observables, at $\sqrt{s_{\rm NN}}\!=\!7.7 \,{\rm GeV}$ in the upcoming RHIC BES-II program will also be presented.