Beam energy dependence of moments of the net-charge multiplicity distributions in Au+Au collisions at RHIC

The STAR collaboration
Phys.Rev.Lett. 113 (2014) 092301, 2014.

Abstract (data abstract)
We report the first measurements of the moments - mean ($M$), variance ($\sigma^{2}$), skewness ($S$) and kurtosis ($\kappa$) - of the net-charge multiplicity distributions at mid-rapidity in Au+Au collisions at seven energies, ranging from $\sqrt{s_{NN}}=$ 7.7 to 200~GeV, as a part of the Beam Energy Scan program at RHIC. The moments are related to the thermodynamic susceptibilities of net-charge, and are sensitive to the location of the QCD critical point. We compare the products of the moments, $\sigma^{2}/M$, $S\sigma$ and $\kappa\sigma^{2}$ with the expectations from Poisson and negative binomial distributions (NBD). The $S\sigma$ values deviate from Poisson and are close to NBD baseline, while the $\kappa\sigma^{2}$ values tend to lie between the two. Within the present uncertainties, our data do not show non-monotonic behavior as a function of collision energy. These measurements provide a valuable tool to extract the freeze-out parameters in heavy-ion collisions by comparing with theoretical models.

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