高能重离子碰撞中喷注输运系数提取的研究进展

Advances in the extraction of jet transport coefficients in high-energy heavy-ion collisions

喷注淬火效应是高能重离子碰撞中产生夸克胶子等离子体新物质形态的硬探针信号,已被大量理论和实验研究所证实.通过大横动量末态强子产额的压低提取量化喷注淬火强度的喷注输运系数q是高能重离子碰撞研究领域的前沿课题.在结合高扭度喷注能量损失的次领头阶微扰量子色动力学部分子模型框架下,本文通过末态强子的压低和实验数据对比提取了介质中心初始最高温度T_(0)处的喷注输运系数q0.不同种类粒子、碰撞能量和碰撞中心度的实验数据对q0的约束表明,q0/T_(0)^(3)会随T 0的增加而降低.为进一步研究q/T_(3)对介质局域温度T(τ,r)的依赖性,本文将RHIC和LHC能区多个中心度的单强子、双强子和γ-强子压低三种观测量的实验数据结合起来,对q/T_(3)(T)进行了整体的限制.面对海量的模型计算,我们首次结合信息场理论的概念设计了先验分布为随机函数的贝叶斯统计推断法,可以削弱q/T_(3)在不同温度区间的长程关联.用低能量非对心碰撞到高能量对心碰撞的实验数据逐步对q/T_(3)(T)进行限制,所得数值结果展示出很强的温度依赖性.

A series of experimental and theoretical studies have detected and confirmed the jet quenching effect as a hard probe signal of the Quark-Gluon Plasma created in high-energy heavy-ion collisions.The jet transport coefficient,denoted asq,can be related to the gluon field strength correlation or the local gluon number density of the strong interaction(QCD)medium along the light-like trajectory of the hard parton,and it quantifies the strength of jet quenching.Theq extraction via suppression of the final state particle is a frontier subject in high-energy heavy-ion collisions.A series of phenomenological studies have made considerable progress in the extraction ofq through model-to-data comparisons using hadron suppression data.Early phenomenological studies generally assumed that theq was proportional to the cubic temperature.Therefore,in this work,with the assumptionq=q0T^(3)/T^(3)_(0),we first extracted theq0,which is the jet transport parameter in the hydrodynamics initial time at the medium highest-temperature T0.The hadron production spectra can be calculated using the next-to-leading order pQCD parton model with higher-twist parton energy loss.With the experimental data of different particle species,colliding energies,and centralities,the numerical results demonstrate that the value of scaledq0/T^(3)0 decreases as the T0 increases.To further study the local temperature dependence ofq/T^(3)in this work,a global constraint onq was performed by combining all existing experimental data on single hadron,dihadron,andγ-hadron suppression at both RHIC and LHC energies across a wide range of centralities.In the face of massive model calculations,we develop an information field(IF)approach to model the prior distribution of the unknown functionq(T),which is free of long-range correlations.Using the IF approach,the data from low-temperature regions cannot constrain theq(T)at higher temperatures.Theq/T^(3)can be constrained progressively when experimental data from more central collisions and higher colliding energies are incrementally included.The global Bayesian analysis using the IF prior provides a stringent constraint onq(T),and the obtainedq/T^(3)exhibits a strong T-dependence.