"Figure 1 (b) 7.7 GeV" 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.本研究报道了相对论重离子对撞机（Relativistic Heavy Ion Collider, RHIC）束流能量扫描（Beam Energy Scan）项目的首批测量结果：针对√s_NN=7.7至200 GeV范围内的7种碰撞能量，测得金核-金核（Au+Au）碰撞快度中点处净电荷多重数分布的各统计矩——均值（M）、方差（σ²）、偏度（S）与峰度（κ）。这些统计矩与净电荷的热力学敏感系数相关，且对量子色动力学（Quantum Chromodynamics, QCD）临界点的位置具有敏感性。我们将各矩的组合量σ²/M、Sσ与κσ²，与泊松分布（Poisson distribution）及负二项分布（Negative Binomial Distribution, NBD）的理论预期进行了对比。Sσ的测量值偏离泊松分布基准，且接近负二项分布的基线结果；而κσ²的测量值则介于两者之间。在当前的实验误差范围内，我们的数据未呈现出随碰撞能量变化的非单调行为。本测量结果可为通过与理论模型对比，提取重离子碰撞中的冻出参数提供一项极具价值的工具。