A unique parametrization of the shapes of secondary dilepton spectra observed in central heavy-ion collisions at CERN-SPS energies

A unique parametrization of secondary (thermal) dilepton yields in heavy-io n experiments at CERN-SPS is proposed. This parametrization resembles a the rmal q (q) over bar annihilation rate. This is inspired by the observation that lepton pair production rates are quantitatively similar, whether expre ssed in a hadronic or partonic basis. Adding the thermal yield and the back ground contributions (hadronic cocktail, Drell-Yan, correlated semileptonic decays of open charm) the spectral shapes of the CERES/NA45, NA38, NA50 an d HELIOS/3 data from experiments with lead and sulfur beams can be well des cribed. (C) 2001 Elsevier Science B.V. All rights reserved.