Production of forward rapidity photons in high energy heavy ion collisions Original Research Article

We consider production of prompt photons in high energy gold–gold and deuteron–gold collisions in the forward rapidity region of RHIC (y∼3.8). In this kinematics, the projectile partons typically have large xbj while the target partons are mostly at very small xbj, so that the primary partonic collisions involve valence quarks from the projectile and gluons from the target. We take the target nucleus to be a color glass condensate while the projectile deuteron or nucleus is treated as a dilute system of partons. We show that the photon production cross section can be written as a convolution of a quark–nucleus scattering cross section, involving a quark–antiquark dipole, with the leading order quark–photon fragmentation function. We consider different models of the quark–antiquark dipole and show that measurement of photons in the forward rapidity region at RHIC can distinguish between different parameterizations of the dipole cross section as well as help clarify the role of parton coalescence models in hadron production at RHIC.