First study of the negative binomial distribution applied to higher moments of net-charge and net-proton multiplicity distributions

A study of the first four moments (mean, variance, skewness, and kurtosis) and their products (κσ2 and Sσ) of the net-charge and net-proton distributions in Au + Au collisions at sNN=7.7-200GeV from HIJING simulations has been carried out. The skewness and kurtosis and the collision volume independent products κσ2 and Sσ have been proposed as sensitive probes for identifying the presence of a QCD critical point. A discrete probability distribution that effectively describes the separate positively and negatively charged particle (or proton and anti-proton) multiplicity distributions is the negative binomial (or binomial) distribution (NBD/BD). The NBD/BD has been used to characterize particle production in high-energy particle and nuclear physics. Their application to the higher moments of the net-charge and net-proton distributions is examined. Differences between κσ2 and a statistical Poisson assumption of a factor of four (for net-charge) and 40% (for net-protons) can be accounted for by the NBD/BD. This is the first application of the properties of the NBD/BD to describe the behavior of the higher moments of net-charge and net-proton distributions in nucleus-nucleus collisions.