A systematic study of direct photon production in heavy ion collisions

A theoretical derivation of photon bremsstrahlung, induced by the interactions of an energetic quark in a hot and dense quark-gluon plasma, is given in the framework of the reaction operator approach. For the physically relevant case of hard jet production, followed by few in-medium interactions. we find that the Landau-Pomeranchuk-Migdal suppression of the bremsstrahlung photon intensity is much stronger than in the previously discussed limit of on-shell quarks and a large number of soft scatterings. This result is incorporated in the first systematic study of direct photon production in minimum bias d + Cu and d + Au and central Cu + Cu and Au + Au heavy ion collisions at the Relativistic Heavy Ion Collider at center of mass energies root s = 62.4 GeV and 200 GeV. We find that the contribution of the photons created via final-state interactions is limited to 35% for 2 GeV < p(T) < 5 GeV and at high transverse momenta the modification of the direct photon cross section is dominated by initial-state cold nuclear matter effects. (C) 2008 Elsevier B.V. All rights reserved.