Beam energy and centrality dependence of the statistical moments of the net-charge and net-kaon multiplicity distributions in Au+Au collisions at STAR

Abstract

In part to search for a possible critical point (CP) in the phase diagram of hot nuclear matter, a Beam Energy Scan was performed at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory. The STAR experiment collected significant Au+Au data sets at beam energies, $\sqrt{{\rm s}_{\rm NN}}$, of 7.7, 11.5, 19.6, 27, 39, 62.4, and 200 GeV. Lattice and phenomenological calculations suggest that the presence of a CP might result in divergences of the thermodynamic susceptibilities and correlation length. The statistical moments of the multiplicity distributions of particles reflecting conserved quantities, such as net-charge and net-strangeness, are expected to depend sensitively on these correlation lengths, making them attractive tools in the search for a possible critical point. The centrality and beam-energy dependence of the statistical moments of the net-charge multiplicity distributions will be discussed. The observables studied include the lowest four statistical moments (mean, variance, skewness, kurtosis) and the products of these moments. The measured moments of the net-kaon multiplicity distributions will also be presented. These will be compared to the predictions from approaches lacking critical behavior, such as the Hadron Resonance Gas model and Poisson statistics.