LHC-ALICE实验相对论重离子对撞中手征磁波和手征涡旋效应的研究

Non-perturbative QCD theory indicates that it is highly likely that the chirality imbalance may exist in the Quark-Gluon Plasma (QGP) created by relativistic heavy-ion collisions. Such chirality anomaly phenomena are also related to local CP violation in strong interaction. Theoretical study suggests that, in the presence of the strong magnetic field produced by the spectators in non-central collisions, the chiral magnetic effect and the chiral separation effect can mutually induce each other, leading to the charge separation along the reaction plane and the formation of the electric quadrupole, which is called Chiral Magnetic Wave (CMW). While in the presence of a global rotation (vorticity), particles with different baryonic charge also tend to separate along reaction plane, which is called Chiral Vortical Effect (CVE)...The experimental measurements of the CMW and the CVE are key topics in the study of chirality, vorticity and strong magnetic field in relativistic heavy-ion collisions. Due to the weak signal and the complicated background, no solid conclusion about the existence of the CMW/CVE has been made so far. This project plans to measure the CMW/CVE signals in Pb-Pb 2.76 TeV and 5.02 TeV collisions at ALICE experiment at LHC, aiming at studying the physics of chirality, vorticity, strong magnetic field and the local CP violation in QGP from the perspective of the experiment. This study could provide evidence and support for the theory, and is of significance to the study of non-perturbative QCD theory as well as the property of QGP.

非微扰QCD理论指出，相对论重离子对撞实验产生的高温高密夸克胶子等离子体中，很可能存在手征非平衡现象，其物理机制与强相互作用下的局域CP破缺紧密相关。理论预言，受非对心碰撞中旁观子产生的强磁场影响，手征磁效应和手征分离效应相互激发，导致系统末态正反电荷粒子分离，产生电四极矩，即手征磁波(CMW)；而在系统涡旋的影响下，不同重子荷粒子会沿反应平面分离，即手征涡旋效应(CVE)。..CMW和CVE的实验测量是研究相对论重离子对撞下手征，涡旋，强磁场和QGP中局域CP破缺的重要课题。由于信号弱，背景复杂，目前尚未在实验中得到系统确认。本项目拟通过ALICE实验，在大型强子对撞机LHC运行的2.76 TeV和5.02 TeV铅-铅对撞中，测量相应的观测量，进行系统的背景排除，旨在寻找手征磁波和手征涡旋效应的信号，从实验角度为理论提供证据和反馈， 这对非微扰QCD理论和研究QGP性质具有重要意义。

理论认为相对论重离子碰撞实验产生的夸克胶子等离子体（QGP）中可能存在手征反常效应，例如手征磁波（CMW）和手征涡旋效应（CVE）等。其物理机制与量子色动力学（QCD）真空的新颖拓扑结构和强相互作用下的局域CP对称性相关，意义十分重大，因此相关的实验测量已成为本领域前沿热点。本项目分析了ALICE实验2.76和5.02 TeV能量铅—铅、质子—铅对撞，以及STAR实验200 GeV能量金—金、质子—金对撞数据，测量了多种粒子的横动量和二阶、三阶各向异性流的电荷不对称依赖，以此探索CMW；并测量了ALICE实验TeV能区铅—铅对撞中重子的γ关联量，以此探索CVE；同时，结合AMPT、PYTHIA、HIJING等模型，研究了强子横动量和各向异性流的电荷不对称依赖；实验和唯象结果均表明了CMW和CVE测量中包含了很大程度的背景贡献，同时部分阐明了可能的背景的动力学机制，比如局域电荷守恒在CMW测量中的贡献。这对深入理解非微扰QCD新颖拓扑结构和QGP的集体运动行为具有重要的科学意义。