Procedure for measuring particle's circular polarization variation with respect to the reaction plane in relativistic heavy-ion collisions

TL;DR

This paper proposes a method to measure how the circular polarization of photons and vector mesons varies with respect to the reaction plane in relativistic heavy-ion collisions, aiming to detect effects of magnetic helicity and chiral anomaly.

Contribution

It introduces a novel procedure for measuring polarization variations relative to the reaction plane in heavy-ion collisions, applicable to photons and vector mesons.

Findings

Proposed differential yield measurement method.

Potential to identify magnetic helicity effects.

Quantification of polarization asymmetries.

Abstract

The EM field pattern created by spectators in relativistic heavy-ion collisions plants a seed of positive (negative) magnetic helicity in the hemisphere above (below) the reaction plane. Owing to the chiral anomaly, the magnetic helicity interacts with the fermionic helicity of the collision system, and causes photons emitted in upper- and lower-hemispheres to have different preferences in the circular polarization. In this paper, we lay down a procedure to measure the variation of the circular polarization w.r.t the reaction plane in relativistic heavy-ion collisions for massless photons, as well as similar polarization patterns for vector mesons decaying into two daughters. We propose to study the yield differentially and compare the yield between upper- and lower-hemispheres in order to identify and quantify such effects.