Large mass diphotons from relativistic heavy ion collisions

We evaluate the production of large mass diphotons from quark annihilation at BNL RHIC and CERN LHC energies from central collisions of gold nuclei. The collision is assumed to lead to either a thermally and chemically equilibrated quark gluon plasma, or a free-streaming quark gluon gas having an identical initial entropy, or a chemically equilibrating quark gluon system, with the same entropy at T = Tc. We also obtain an estimate of hard photon pairs from initial state quark annihilation and find that the thermal production dominates the yield up to M ≈ 4 GeV at RHIC, and up to 6 GeV at LHC. A simulation study of decay versus thermal diphotons is presented.