Anisotropy of Low Energy Direct Photons in Relativistic Heavy Ion Collisions

TL;DR

This paper studies the angular distribution of low energy photons emitted during relativistic heavy ion collisions, revealing initial geometric configurations and anisotropic flow behavior that differ from hadronic signals.

Contribution

It introduces a Wigner function approach to analyze low energy photon anisotropy, highlighting differences from hadronic flow patterns.

Findings

Photon $v_{2}$ increases as photon energy decreases

Photon angular distribution encodes initial geometric information

Distinct behavior of photon $v_{2}$ compared to hadrons

Abstract

We investigate the behavior of low energy photons radiated by the deceleration processes of two colliding nuclei in relativistic heavy ion collisions using the Wigner function approach for electromagnetic radiation fields. The angular distribution reveals the information of the initial geometric configurations. Such a property is reflected in the anisotropic parameter $v_{2}$, showing an increasing $v_{2}$ as energy decreases, which is a behavior qualitatively different from $v_{2}$ from hadrons produced in the collisions.