The chiral magnetic effect (CME) in quantum chromodynamics (QCD) refers to a charge separation (an electric current) of chirality imbalanced quarks generated along an external strong magnetic field. The chirality imbalance results from interactions of quarks, under the approximate chiral symmetry restoration, with metastable local domains of gluon fields of non-zero topological charges out of QCD vacuum fluctuations. Those local domains violate the $\mathcal{P}$ and $\mathcal{CP}$ invariance, potentially offering a solution to the strong $\mathcal{CP}$ problem in explaining the magnitude of the matter-antimatter asymmetry in today's universe. Relativistic heavy-ion collisions, with the likely creation of the high energy density quark-gluon plasma and restoration of the approximate chiral symmetry, and the possibly long-lived strong magnetic field, provide a unique opportunity to detect the CME. Early measurements of the CME-induced charge separation in heavy-ion collisions are dominated by physics backgrounds. Major efforts have been devoted to eliminate or reduce those backgrounds. We review those efforts, with a somewhat historical perspective, and focus on the recent innovative experimental undertakings in the search for the CME in heavy-ion collisions.

中文翻译：

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重离子碰撞手征磁效应的实验研究

量子色动力学 (QCD) 中的手性磁效应 (CME) 是指沿外部强磁场产生的手性不平衡夸克的电荷分离（电流）。手性不平衡是由于夸克在近似手性对称恢复下与来自 QCD 真空涨落的非零拓扑电荷胶子场的亚稳态局部域的相互作用造成的。这些局部域违反了 $\mathcal{P}$ 和 $\mathcal{CP}$ 不变性，可能为强 $\mathcal{CP}$ 问题提供解决方案，以解释当今宇宙中物质 - 反物质不对称的程度. 相对论重离子碰撞，可能会产生高能量密度的夸克-胶子等离子体并恢复近似手性对称性，以及可能长期存在的强磁场，为检测 CME 提供了独特的机会。重离子碰撞中 CME 引起的电荷分离的早期测量主要由物理背景决定。为消除或减少这些背景作出了重大努力。我们从某种历史的角度回顾了这些努力，并关注最近在重离子碰撞中寻找 CME 的创新实验工作。