Anisotropy of photon production: Initial eccentricity or magnetic field

TL;DR

This paper investigates whether the strong azimuthal anisotropy of direct photons in heavy-ion collisions is primarily caused by magnetic fields in the early collision stage, challenging existing assumptions about photon production.

Contribution

It proposes an experimental method to determine the magnetic field's role in photon anisotropy, offering new insights into early collision dynamics.

Findings

Potential to clarify the magnetic field's influence on photon anisotropy

May alter understanding of thermalization in heavy-ion collisions

Provides a new experimental approach for collision analysis

Abstract

Recent measurements of the azimuthal anisotropy of direct photons in heavy-ion collisions at the energies of RHIC show that it is of the same order as the hadronic one. This finding appears to contradict the expected dominance of photon production from a quark-gluon plasma at an early stage of a heavy-ion collision. A possible explanation of the strong azimuthal anisotropy of the photons, given recently, is based on the presence of a large magnetic field in the early phase of a collision. In this letter, we propose a method to experimentally measure the degree to which a magnetic field in heavy-ion collisions is responsible for the observed anisotropy of photon production. The experimental test proposed in this letter may potentially change our understanding of the non-equilibrium stage and possible thermalization in heavy-ion collisions.