We compute the radiation of lepton pairs by the quarks during a central collision between gold nuclei at energy of the Brookhaven Relativistic Heavy Ion Collider (√s =200A GeV) within the parton cascade model. The distribution of radiated pairs evolves smoothly from the initial Drell-Yan type reactions all the way towards equilibrium radiation. Contributions from reactions involving secondary partons dominate the Drell-Yan yield by at least a factor of 5 even at an invariant mass of 8 GeV. Therefore, experiments can test the evolution of partons towards thermal equilibrium at these energies.

• Received 27 October 1992

DOI:https://doi.org/10.1103/PhysRevLett.70.1920