# Centrality dependence of photon yield and elliptic flow from gluon fusion and splitting induced by magnetic fields in relativistic heavy-ion collisions

## TL;DR

This paper investigates how magnetic fields in relativistic heavy-ion collisions influence photon production and elliptic flow, showing that magnetic effects help explain experimental data at RHIC energies.

## Contribution

It introduces a calculation of photon yield and elliptic flow from gluon fusion and splitting processes induced by magnetic fields, accounting for early-time magnetic field dynamics and gluon saturation.

## Key findings

- Magnetic field effects increase photon yield and elliptic flow at low transverse momentum.
- The model improves agreement with RHIC photon data across centralities.
- Magnetic contributions help reconcile discrepancies between data and hydrodynamic models.

## Abstract

We compute the photon yield and elliptic flow coefficient in relativistic heavy-ion collisions from gluon fusion and splitting processes induced by a magnetic field for different centralities. The calculation accounts for the intense magnetic field and the high gluon occupation number at early times. The photon production induced by these process represents an excess contribution 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 $v_2$. The time evolution of the field strength and reaction volume is computed using UrQMD. We show that with reasonable values for the saturation scale, the calculation helps to better describe the experimental results obtained at RHIC energies for the lowest part of the transverse photon momentum at different centralities.