DIPHOTON RATES FROM THERMALIZED MATTER RESULTING IN ULTRA-RELATIVISTIC HEAVY-ION COLLISIONS

Diphoton radiation off strongly interacting matter resulting from ultr arelativistic heavy-ion collisions is estimated for SPS and RHIC condi tions. At SPS energies the thermal diphoton signal competes strongly w ith the Drell - Yan like background, For RHIC energies we find that ra diation from initially undersaturated (but gluon-rich) deconfined matt er overwhelms the hadron gas at invariant mass M > 1 GeV; the Drell - Yan like diphotons dominate at M > 2.5 GeV. Due to this the so-called M-perpendicular to scaling is approximately obtained in a narrow windo w and can serve as additional tool for discriminating radiation from q uark-gluon matter.