AGH University of Science and Technology, Cracow, Poland.
University of Kentucky, Lexington, Kentucky 40506-0055, USA.
Phys Rev Lett. 2014 Aug 29;113(9):092301. doi: 10.1103/PhysRevLett.113.092301. Epub 2014 Aug 26.
We report the first measurements of the moments--mean (M), variance (σ(2)), skewness (S), and kurtosis (κ)--of the net-charge multiplicity distributions at midrapidity in Au+Au collisions at seven energies, ranging from sqrt[sNN]=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, σ(2)/M, Sσ, and κσ(2), with the expectations from Poisson and negative binomial distributions (NBDs). The Sσ values deviate from the Poisson baseline and are close to the NBD baseline, while the κσ(2) values tend to lie between the two. Within the present uncertainties, our data do not show nonmonotonic 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.
我们报告了在 RHIC 的 Beam Energy Scan 项目中，在七个能量范围内，从 sqrt[sNN]=7.7 到 200GeV，对 Au+Au 碰撞中中快度处净电荷多重数分布的矩——平均值（M）、方差（σ(2)）、偏度（S）和峰度（κ）——的首次测量结果。这些矩与净电荷的热力学量有关，对 QCD 临界点的位置敏感。我们将矩的乘积 σ(2)/M、Sσ 和 κσ(2)与泊松分布和负二项分布（NBD）的预期进行了比较。Sσ 值偏离泊松基线，接近 NBD 基线，而 κσ(2) 值则倾向于介于两者之间。在目前的不确定性范围内，我们的数据没有显示出随碰撞能量的非单调行为。这些测量结果为通过与理论模型比较来提取重离子碰撞中的冻结参数提供了一个有价值的工具。
