# Azimuthal Asymmetry of Direct Photons in High Energy Nuclear Collisions

## TL;DR

This paper predicts a significant azimuthal asymmetry in direct photon production in non-central high energy nuclear collisions, which could serve as a signature of quark-gluon plasma formation.

## Contribution

It introduces the concept that jet-plasma interactions produce a measurable photon azimuthal asymmetry with a phase shift, highlighting a new observable for quark-gluon plasma detection.

## Key findings

- Predicted negative v_2 for direct photons in non-central collisions
- Identified phase difference between photon and hadron anisotropies
- Suggested photon asymmetry as a signature of quark-gluon plasma

## Abstract

We show that a sizeable azimuthal asymmetry, characterized by a coefficient v_2, is to be expected for direct photons produced in non-central high energy nuclear collisions. This signal is generated by photons radiated by jets interacting with the surrounding hot plasma. The anisotropy is out of phase by an angle $\pi/2$ with respect to that associated with the elliptic anisotropy of hadrons, leading to negative values of v_2. Such an asymmetry, if observed, could be a signature for the presence of a quark gluon plasma and would establish the importance of jet-plasma interactions as a source of electromagnetic radiation.