Non-monotonic energy dependence of net-proton number fluctuations

Abstract

Non-monotonic variation with collision energy ($\sqrt{s_{\mathrm{NN}}}$) of the moments of the net-baryon number distribution in heavy-ion collisions, related to the correlation length and the susceptibilities of the system, is suggested as a signature for the Quantum Chromodynamics (QCD) critical point. We report the first evidence of a non-monotonic variation in kurtosis times variance of the net-proton number (proxy for net-baryon number) distribution as a function of \rootsnn with 3.1$\ddot{I}ƒ$ significance, for head-on (central) gold-on-gold (Au+Au) collisions measured using the STAR detector at RHIC. Data in non-central Au+Au collisions and models of heavy-ion collisions without a critical point show a monotonic variation as a function of $\sqrt{s_{\mathrm{NN}}}$.

12 Pages, 9 Figures and 5 Tables (published version)