Experimental study of local strong parity violation in relativistic nuclear collisions

TL;DR

This paper investigates local strong parity violation in relativistic nuclear collisions by analyzing charge separation signals in heavy ion collisions, providing experimental evidence consistent with theoretical predictions of parity-odd domains.

Contribution

It presents the first experimental analysis of charge separation effects using three-particle correlators in heavy ion collisions, supporting the existence of local parity violation in QCD.

Findings

Detection of charge separation signals consistent with parity violation

Existing models fail to fully explain the observed effects

Results suggest new physics beyond current event generators

Abstract

Parity-odd domains, corresponding to non-trivial topological solutions of the QCD vacuum, might be created in relativistic heavy ions collisions. These domains are predicted to lead to charge separation along the system orbital momentum of the system created in non-central collisions. Three-particle mixed harmonics azimuthal correlator is a \P even observable but directly sensitive to the charge separation effect. Using this observable to analyze Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}=200$ and 62 GeV, STAR detects a signal consistent with several of the theoretical expectations. Possible contributions from effects not related to parity violation are studied with existing event generators, which fail to describe the data. Future directions in studying the effect are discussed.