Dilepton signal from an ultrahigh-temperature quark-gluon plasma

Collisions between ultrarelativistic nuclei can result in an ultrarelativistic hot quark-gluon plasma with perfect-gas properties. The inevitable hydrodynamic expansion of this plasma and the accompanying cooling of matter are used to find the resulting momentum distribution of thermal dileptons (heavy photons). The dilepton distribution integrated over the masses is also obtained. Comparison with the inclusive distribution of individual charged leptons, obtained earlier by a similar method, is then used to analyze the diagnostic content of the electromagnetic signal under real conditions (taking expansion into account)