# Prompt photon yield and elliptic flow from gluon fusion induced by magnetic fields in relativistic heavy-ion collisions

## TL;DR

This paper investigates early-time photon production in heavy-ion collisions caused by gluon fusion facilitated by magnetic fields, showing it can explain experimental photon yields and elliptic flow better than previous models.

## Contribution

It introduces a novel gluon fusion mechanism induced by magnetic fields for photon production, addressing a gap in understanding early-time electromagnetic signals in heavy-ion collisions.

## Key findings

- The magnetic field enables gluon fusion, increasing photon yield.
- The model improves agreement with RHIC photon data.
- The approach accounts for early-time collision dynamics.

## Abstract

We compute photon production at early times in semi-central relativistic heavy-ion collisions from non-equilibrium gluon fusion induced by a magnetic field. The calculation accounts for the main features of the collision at these early times, namely, the intense magnetic field and the high gluon occupation number. The gluon fusion channel is made possible by the magnetic field and would otherwise be forbidden due to charge conjugation invariance. Thus, the photon yield from this process is an excess over calculations without magnetic field effects. We compare this excess to the difference between PHENIX data and recent hydrodynamic calculations for the photon transverse momentum distribution and elliptic flow coefficient $v_2$. We show that with reasonable values for the saturation scale and magnetic field strength, the calculation helps to better describe the experimental results obtained at RHIC energies for the lowest part of the transverse photon momentum.