The effects of topological charge change in heavy ion collisions: "Event by event P and CP violation"

TL;DR

This paper discusses how topological configurations in QCD can lead to charge separation in heavy ion collisions via the Chiral Magnetic Effect, potentially observable as evidence of CP violation and the topological nature of the QCD vacuum.

Contribution

It introduces a novel mechanism linking topological charge changes to charge separation in heavy ion collisions through the Chiral Magnetic Effect.

Findings

Large magnetic fields in collisions can induce charge separation.

The effect could be experimentally observable.

Charge separation serves as evidence of QCD topological effects.

Abstract

Quantum chromodynamics (QCD) contains field configurations which can be characterized by a topological invariant, the winding number Q_w. Configurations with nonzero Q_w break the charge-parity CP symmetry of QCD. We consider a novel mechanism by which these configurations can separate charge in the presence of a background magnetic field - the "Chiral Magnetic Effect". We argue that sufficiently large magnetic fields are created in heavy ion collisions so that the Chiral Magnetic Effect causes preferential emission of charged particles along the direction of angular momentum. Since separation of charge is CP-odd, any observation of the Chiral Magnetic Effect could provide a clear demonstration of the topological nature of the QCD vacuum. We give an estimate of the effect and conclude that it might be observed experimentally.