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

Abstract

We compute photon production at early times in semicentral relativistic heavy-ion collisions from nonequilibrium 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 us better describe the experimental results obtained at RHIC energies for the lowest part of the transverse photon momentum.