利用STAR同量异位素核碰撞测量核结构中子皮及寻找手征磁效应

量子色动力学QCD预言手征磁效应CME的存在，在相对论重离子碰撞中引起正负电荷分离，但其实验测量包含很大的各向异性流物理本底，为更好地测量CME，RHIC运行了同量异位素核钌-钌和锆-锆碰撞实验，预期它们具有相同的物理本底。但我们发现原子核结构对重离子碰撞具有重要影响，造成不同各向异性流物理本底，同时发现粒子多重数分布可以较精确地确定中子皮厚度和对称能大小，辅助补充低能核物理在这方面的实验研究。本项目拟利用STAR实验同量异位素核碰撞数据测量中子皮和对称能，确定钌和锆的核结构；并在此基础上通过匿情分析和我们团队原创的分析方法寻找CME。本项目同时支撑湖州师范学院的STAR实验运行、数据采集和刻度工作。本项目将是首次利用高能核碰撞确定原子核结构，是一个崭新的交叉学科方向，中子皮和对称能一直是核物理领域亟待解决的问题，物理意义重大；手征磁效应是QCD的基本物理原理，其实验发现具有重要科学意义。

Quantum Chromodynamics (QCD) predicts the existence of the chiral magnetic effect (CME), which induces charge separation in relativistic heavy ion collisions. Charge separation measurements, however, contain a major physics background due to anisotropic flow. To better measure CME, isobar Ru-Ru and Zr-Zr collisions have been conducted where the physics backgrounds are expected to be the same. We have found, however, that nuclear structure has important influence on relativistic heavy ion collisions, causing non-identical flow backgrounds. We have also found that particle multiplicity distributions in isobar collisions can yield a relatively precise measurement of the neutron skin thickness (and thus the symmetry energy) in nuclei, supplemental to low energy nuclear experiments. This project proposes to use the STAR isobar data to measure the neutron skin and symmetry energy, and determine the Ru and Zr nuclear structures. With the knowledge of the isobar nuclear structures, we will further search for the CME by blind analysis using our innovative analysis methods, to answer the burning question whether CME exists and how large a signal it is. The project will also support Huzhou University's experimental work on STAR, including data taking shifts and calibration. This project will be the first time when high energy nuclear collisions are used to determine nuclear structures, a newly developing interdisciplinary research direction. The neutron skin and symmetry energy has been a long pursued problem in nuclear physics, and is highly important. The CME is a fundamental physics in QCD, and its experimental discovery is of paramount significance.