重离子碰撞中的矢量介子自旋排列  

Global spin alignment of vector mesons in heavy ion collisions

作　　者：盛欣力 梁作堂 王群[3] Sheng Xin-Li;Liang Zuo-Tang;Wang Qun(INFN-Firenze,Via Giovanni Sansone,1,50019 Sesto Fiorentino FI,Italy;Key Laboratory of Particle Physics and Particle Irradiation,Ministry of Education,Institute of Frontier and Interdisciplinary Science,Shandong University,Qingdao 266237,China;Department of Modern Physics,University of Science and Technology of China,Hefei 230026,China)

机构地区：[1]INFN-Firenze,Via Giovanni Sansone,1,50019 Sesto Fiorentino FI,Italy [2]山东大学前沿交叉科学青岛研究院,青岛266237 [3]中国科学技术大学近代物理系,合肥230026

出　　处：《物理学报》2023年第7期127-137,共11页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:12135011,11890713)资助的课题.

摘　　要：在非对心相对论重离子碰撞中,参与反应的系统具有巨大的轨道角动量,从而使产生的夸克胶子等离子体具有极强涡旋场,并通过自旋-轨道相互作用导致部分子的自旋极化,经过强子化导致重子的自旋极化以及矢量介子的自旋排列等可观测效应.矢量介子的自旋排列是指其自旋密度矩阵的00元素ρ00偏离1/3.在矢量介子衰变到两个赝标介子的过程中,衰变产物的极角分布只与ρ00有关,以此可以对自旋排列进行测量.理论研究表明,重离子碰撞过程中,重子的自旋极化反映了夸克自旋极化的时空平均效应,而矢量介子自旋排列则反映了夸克反夸克自旋极化的局域相空间关联.本文回顾了相对论重离子碰撞中矢量介子自旋排列的相关理论工作.重点以非相对论夸克融合模型为例,明确地计入夸克极化的相空间依赖性,展示了矢量介子自旋排列与夸克反夸克自旋极化特别是它们之间相空间关联的关系.本文还讨论了涡旋、电磁场、有效ø介子场以及它们的局域涨落对ø介子自旋排列的贡献,结果显示强作用场的时空关联效应是导致ø介子自旋排列的主要因素.矢量介子自旋排列为探索强相互作用物质和强相互作用场的性质提供了新途径.In non-central relativistic heavy-ion collisions,the large initial orbital angular momentum results in strong vorticity fields in the quark-gluon plasma,which polarize partons through the spin-orbit coupling.The global polarization of quark matter will be converted to the global polarization of baryons and the global spin alignment of vector mesons.The spin alignment refers to the ρ00 element of the spin density matrix for vector mesons.When a vector meson decays to two pseudoscalar mesons,the polar angle distribution for the decay product depends on ρ00,through which the spin alignment can be measured.Theoretical studies show that the global spin polarization of baryons reflects the space-time average of the quark polarization,while the spin alignment of vector mesons reflects the local phase space correlation between the polarization of quark and antiquark.In this article,we review recent theoretical works about the spin alignment of vector mesons.We consider a non-relativistic quark coalescence model in spin and phase space.Within this model,the spin alignment of the vector meson can be described through the phase space correlation of quark's and antiquark's polarization.The contributions to the spin alignment of ø mesons from vorticity fields,electromagnetic fields,and effective ø meson fields are discussed.The spin alignment of vector mesons opens a new window for the properties of strong interaction fields in heavy-ion collisions.

关 键 词：整体极化效应 矢量介子自旋排列 自旋轨道耦合 夸克融合模型 重离子碰撞 

分 类 号：O571.6[理学—粒子物理与原子核物理]