Azimuthal Charged-Particle Correlations and Possible Local Strong Parity Violation

TL;DR

This paper investigates charge separation effects in heavy ion collisions, using a three-particle azimuthal correlator sensitive to local strong parity violation, and reports measurements consistent with theoretical predictions.

Contribution

It introduces a new three-particle correlator to detect local parity violation effects in heavy ion collisions and provides experimental measurements supporting this phenomenon.

Findings

Detected signals consistent with local parity violation theories

Measured charge separation in Au+Au and Cu+Cu collisions at 200 GeV

Discussed alternative effects that could mimic the signal

Abstract

Parity-odd domains, corresponding to non-trivial topological solutions of the QCD vacuum, might be created during relativistic heavy ion collisions. These domains are predicted to lead to charge separation of quarks along the system's orbital momentum axis. We investigate a three particle azimuthal correlator which is a \P even observable, but directly sensitive to the charge separation effect. We report measurements of charged hadrons near center-of-mass rapidity with this observable in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}$=200 GeV using the STAR detector. A signal consistent with several expectations from the theory is detected. We discuss possible contributions from other effects that are not related to parity violation.