# Experimental searches for the chiral magnetic effect in heavy-ion collisions

## TL;DR

This paper reviews experimental efforts to detect the chiral magnetic effect in heavy-ion collisions, focusing on overcoming background signals to identify genuine CME-induced charge separation.

## Contribution

It provides a comprehensive review of recent innovative experimental techniques and background mitigation strategies in the search for the CME in heavy-ion collisions.

## Key findings

- Early measurements dominated by background physics
- Development of methods to reduce or eliminate backgrounds
- Recent experimental efforts show progress in CME detection

## Abstract

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.