The PT dependence of dilepton production in nuclear collisions

The PT distribution of massive lepton pairs produced in hadron-nucleus (h-A) collisions becomes broader with increasing A. In a framework based on perturbative QCD, this effect can be interpreted as elastic initial-state parton scattering, and it is predicted to saturate for large A. We show that an extrapolation of this behaviour to nucleus-nucleus collisions is in accord with measured continuum (Drell-Yan) dilepton behaviour, but that it cannot account for the PT dependence of J/Ψ suppression. Consequently, the behaviour of J/Ψ/D-Y in the large-ET region of nuclear collisions provides a crucial test for the production of a quark-gluon plasma. (orig.)