Dilepton production in nuclear collisions

Dilepton production rates in nuclear collisions are calculated in order to study their sensitivity to the quark-gluon plasma and to the hadronic phases. This treatment differs from previous work on the subject in two respects: The width of the rho-meson, being exchanged in ππ annihilation, is made temperature dependent, thus taking into account resonance melting as the critical deconfinement temperature Td is approached. Secondly, we study in addition to the standard scenario where chiral symmetry restoration and deconfinement occur at the same temperature (Tc=Td), an alternative possibility where deconfinement preceeds chiral symmetry restoration (Td < Tc). Results differ substantially from those obtained assuming a temperature independent rho-meson width, and Tc=Td. (orig.)