"Without CBWC 2.5% step width at 19.6 GeV" of "Cumulants and Correlation Functions of Net-proton, Proton and Antiproton Multiplicity Distributions in Au+Au Collisions at RHIC"

We report a systematic measurement of cumulants, $C_{n}$, for net-proton, proton and antiproton, and correlation functions, $\kappa_n$, for proton and antiproton multiplicity distributions up to the fourth order in Au+Au collisions at $\sqrt{s_{\mathrm {NN}}}$ = 7.7, 11.5, 14.5, 19.6, 27, 39, 54.4, 62.4 and 200 GeV. The $C_{n}$ and $\kappa_n$ are presented as a function of collision energy, centrality and kinematic acceptance in rapidity, $y$, and transverse momentum, $p_{T}$. The data were taken during the first phase of the Beam Energy Scan (BES) program (2010 -- 2017) at the Relativistic Heavy Ion Collider (RHIC) facility. The measurements are carried out at midrapidity ($|y| <$ 0.5) and transverse momentum 0.4 $<$ $p_{\rm T}$ $<$ 2.0 GeV/$c$, using the STAR detector at RHIC. We observe a non-monotonic energy dependence ({\snn} = 7.7 -- 62.4 GeV) of the net-proton $C_{4}$/$C_{2}$ with the significance of 3.1$\sigma$ for the 0-5\% central Au+Au collisions. This is consistent with the expectations of critical fluctuations in a QCD-inspired model. Thermal and transport model calculations show a monotonic variation with \snn. For the multiparticle correlation functions, we observe significant negative values for a two-particle correlation function, $\kappa_2$, of protons and antiprotons, which are mainly due to the effects of baryon number conservation. Furthermore, it is found that the four-particle correlation function, $\kappa_4$, of protons plays a role in determining the energy dependence of proton $C_4/C_1$ below 19.6 GeV, which cannot be solely understood by the negative values of $\kappa_2$ for protons.

本工作报道了质心系能量√s_NN为7.7、11.5、14.5、19.6、27、39、54.4、62.4及200 GeV的金金（Au+Au）碰撞中，净质子、质子与反质子的累积量（cumulants）Cₙ，以及质子和反质子多重数分布的关联函数（correlation functions）κₙ的系统测量结果，测量阶数最高至四阶。上述Cₙ与κₙ以碰撞能量、碰撞中心度、快度（rapidity）y与横向动量（transverse momentum）p_T的运动学接收度为变量进行展示。本数据集采集自相对论重离子对撞机（Relativistic Heavy Ion Collider, RHIC）设施的束流能量扫描（Beam Energy Scan, BES）一期项目（2010年至2017年）。本次测量利用RHIC上的STAR探测器完成，测量覆盖快度区间|y|<0.5，横向动量范围为0.4 < p_T < 2.0 GeV/c。针对0-5%中心度的金金碰撞，我们观测到净质子的C₄/C₂比值呈现出非单调的能量依赖关系（√s_NN为7.7至62.4 GeV），其统计显著性达3.1σ。该结果与基于量子色动力学（Quantum Chromodynamics, QCD）的模型所预言的临界涨落预期一致。热模型与输运模型的计算结果则显示其随√s_NN呈单调变化。对于多粒子关联函数，我们观测到质子与反质子的两粒子关联函数κ₂存在显著的负值，这一现象主要源于重子数守恒效应。此外，我们发现在√s_NN低于19.6 GeV的能区，质子的四粒子关联函数κ₄对质子C₄/C₁比值的能量依赖关系存在显著影响，而仅用质子的κ₂负值无法完全解释这一行为。