Direct Photons at SPS and RHIC Energies
McGill U., Canada
The production of real and virtual photons in relativistic heavy-ion collisions is studied. Low-pT photons, dominated by hadron gas contributions, are evaluated within a massive Yang-Mills approach. Earlier calculations are reexamined with additional constraints, including new production channels and form-factors. The intermediate to high-pT region is dominated by the physics of jets. A treatment, complete to leading-order in the strong coupling, is used to calculate energy loss in the strongly interacting medium. This approach is convolved with a physical description of the initial spatial distribution of jets and with an expansion of the emission zone. The role played by jet-plasma interactions is highlighted, showing that they dominate in the range 2 < pT < 4 GeV, at the Relativistic Heavy Ion Collider (RHIC). This mechanism has an important impact on both the total photon yield and the photon elliptic flow.