Beam Energy Dependence of Higher Moments of Net-proton Multiplicity Distributions in Heavy-ion Collisions at RHIC

TL;DR

This study measures higher moments of net-proton distributions in heavy-ion collisions across various energies at RHIC, revealing deviations from Poisson expectations and providing insights into the underlying physics.

Contribution

It presents the first comprehensive analysis of higher moments of net-proton distributions over a wide energy range at RHIC, including methods to reduce centrality resolution effects.

Findings

Deviations from Poisson expectations in central collisions at all energies.

Higher moments are sensitive to correlation length and baryon number susceptibility.

Comparison with transport models helps distinguish critical physics effects.

Abstract

We present various order moments (Variance ($\sigma^2$), Skewness($S$), Kurtosis($\kappa$)) of net-proton multiplicity distributions in Au+Au collisions from the first phase of RHIC beam energy scan ({\sNN}=7.7$-$200 GeV). The measurements are carried out by the STAR detector at mid-rapidity ($|y|<0.5$) and within transverse momentum range $0.4<p_{T}<0.8$ {\gevc}. The product of moments ({\SD} and \KV) are predicted to be sensitive to the correlation length and connected to ratios of baryon number susceptibility. We observe deviations below Poisson expectations in the most central collisions for all of the energies. These results are compared with a transport model to understand the effects not related to critical physics. We also discuss the error estimation methods and the techniques to suppress centrality resolution effect in the moment analysis.