"Figure 4 (c)" of "Beam energy dependence of moments of the net-charge multiplicity distributions in Au+Au collisions at RHIC"

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.

我们报道了首个针对7个不同碰撞能量下金-金（Au+Au）碰撞中心快度区净电荷多重数分布的矩的测量结果，这些矩涵盖均值（$M$）、方差（$sigma^2$）、偏度（$S$）与峰度（$kappa$），碰撞能量范围为$sqrt{s_{NN}}=7.7$~200吉电子伏特（GeV），该项工作属于相对论重离子对撞机（RHIC）束流能量扫描计划的一部分。这些矩与净电荷的热力学敏感度相关，且对量子色动力学（QCD）临界点的位置具有敏感性。我们将矩的组合$sigma^2/M$、$Ssigma$与$kappasigma^2$分别与泊松分布以及负二项分布（NBD）的理论预期进行了对比。其中$Ssigma$的测量值偏离泊松分布基准，且与负二项分布的预期较为接近；而$kappasigma^2$的测量值则介于两者之间。在当前的不确定性范围内，我们的实验数据未呈现出随碰撞能量变化的非单调行为。通过与理论模型进行对比，这些测量结果为提取重离子碰撞中的冻结参数提供了极具价值的工具。