摘要
相对论重离子对撞机(Relativistic Heavy Ion Collider,RHIC)-STAR(Solenoid Tracker at RHIC)实验测量了√s_(NN)=7.7~200 GeV能量下Au+Au碰撞中的净质子(净重子的代表)、净电荷和净K介子(净奇异数的代表)多重数分布的累积量,发现净质子四阶累积量与二阶累积量之比(κσ^(2))呈现出了非单调的能量依赖性行为。在相对论重离子碰撞实验中只能测到末态粒子的信息。因此,基于多相输运(A Multi-Phase Transport,AMPT)模型对Au+Au碰撞系统中守恒荷(重子数、电荷数和奇异数)的涨落性质进行了研究,发现AMPT模型的结果基本能描述RHIC-STAR实验结果。更重要的是,利用AMPT模型了解了相对论重离子碰撞动力学演化过程中几个关键效应(守恒荷粒子的产生和扩散、强子化、强子再散射和弱衰变)对守恒荷涨落演化及其粒子关联函数的影响。发现正负电荷之间关联可能源于弦熔化机制,重子(质子)关联函数符合重子数守恒期望,奇异数(净K介子)的关联函数源于对产生,这些代表量与守恒荷的对应关系行为上定性一致,但数量不同。虽然AMPT模型目前缺乏临界涨落机制,但我们的结果可以为守恒荷涨落的研究提供一条基线,这有助于在相对论重离子碰撞中寻找量子色动力学(Quantum Chromodynamics,QCD)临界点(Critical End Point,CEP)附近可能的临界行为。初步在模型中考虑临界密度涨落,结果发现它起着一定的作用。
The RHIC-STAR(Relativistic Heavy Ion Collider-Solenoid Tracker at RHIC)experiments have measured the cumulants of net-proton(a proxy for net-baryon),net-charge,and net-kaon(proxy of net-strangeness)multiplicity distributions in Au+Au collisions at different centers of mass with energies ranging from 7.7 GeV to 200 GeV.Recent results have shown that the ratio of the fourth-order net-proton cumulant over the second-order one(κσ^(2))exhibits a nonmonotonic energy dependence.In relativistic heavy-ion collision experiments,only information about the final state particles can be measured.Therefore,we investigated the fluctuations of the conserved charges(baryon,electric charge,and strangeness)in Au+Au collisions using a multiphase transport(AMPT)model.This model can basically describe the results measured by the RHIC-STAR experiment.More importantly,the AMPT model is used to understand the key impacts of the dynamical evolution of relativistic heavy-ion collisions on fluctuations and correlation functions,including the creation and diffusion of conserved charges,hadronization,hadronic rescatterings,and weak decays.It was discovered that the correlation between positive and negative charges may originate from the string melting mechanism.Baryon(proton)correlation functions are consistent with the expectation of baryon number conservation.Net-strangeness(net-kaon)originates from pair production.We studied the correspondence between representative quantities and their conserved charges and found that their behaviors are qualitatively consistent yet quantitatively different.Although the physics of quantum chromodynamics(QCD)critical fluctuations is not included in the AMPT model,our results are expected to provide a baseline for the search of possible critical behavior at the QCD critical end point in relativistic heavy-ion collisions.We incorporated critical density fluctuations into the model and found that they play a role.
作者
陈倩
马国亮
陈金辉
CHEN Qian;MA Guoliang;CHEN Jinhui(Key Laboratory of Nuclear Physics and Ion-beam Application(MOE),Institute of Modern Physics,Fudan University,Shanghai 200433,China;Shanghai Research Center for Theoretical Nuclear Physics,NSFC and Fudan University,Shanghai 200438,China;Shanghai Institute of Applied Physics,Chinese Academy of Sciences,Shanghai 201800,China;University of Chinese Academy of Sciences,Beijing 100049,China)
出处
《核技术》
CAS
CSCD
北大核心
2023年第4期176-203,共28页
Nuclear Techniques
基金
国家重点研发计划(No.2022YFA1604900)
国家自然科学基金(No.12147101,No.11890714,No.11835002,No.11961131011,No.11421505)
中国科学院战略优先研究计划(No.XDB34030000)
广东省基础与应用基础研究重大项目(No.2020B0301030008)资助。
关键词
守恒荷
涨落
累积量
关联函数
QCD相变
临界点
Conserved charge
Fluctuation
Cumulants
Correlation functions
QCD phase transition
Critical end point(CEP)
