Higher Moments of Net Proton Multiplicity Distributions at RHIC

Abstract

We report the first measurements of the kurtosis ($\ensuremath{\kappa}$), skewness ($S$), and variance (${\ensuremath{\sigma}}^{2}$) of net-proton multiplicity (${N}_{p}\ensuremath{-}{N}_{\overline{p}}$) distributions at midrapidity for $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{{s}_{NN}}=19.6$, 62.4, and 200 GeV corresponding to baryon chemical potentials (${\ensuremath{\mu}}_{B}$) between 200 and 20 MeV. Our measurements of the products $\ensuremath{\kappa}{\ensuremath{\sigma}}^{2}$ and $S\ensuremath{\sigma}$, which can be related to theoretical calculations sensitive to baryon number susceptibilities and long-range correlations, are constant as functions of collision centrality. We compare these products with results from lattice QCD and various models without a critical point and study the $\sqrt{{s}_{NN}}$ dependence of $\ensuremath{\kappa}{\ensuremath{\sigma}}^{2}$. From the measurements at the three beam energies, we find no evidence for a critical point in the QCD phase diagram for ${\ensuremath{\mu}}_{B}$ below 200 MeV.