Dilepton production in a chemically equilibrating, expanding, and hadronizing quark-gluon plasma

Dilepton production is considered within a complete dynamical framework for thermalized matter assumed to be formed in ultrarelativistic heavy-ion collisions. Our model includes (i) chemical equilibration processes in the initially gluon enriched plasma, (ii) longitudinal as well as transverse expansion, and (iii) the hadronization through a mixed phase. Besides the basic electromagnetic quark\char21{}antiquark annihilation process we also take into account the QCD Compton-like and annihilation processes for calculating the dilepton rate in the deconfined phase, while in the hadronic stage we employ a parametrization of the effective form factor which is based on the complete set of meson decays and reactions. We find that, due to the transverse expansion of the matter, the dilepton yield from the hadron gas is strongly reduced and, therefore, the deconfined matter gives the dominant contribution in case of initial conditions which are expected to be achieved at RHIC. This provides the basis for the ${\mathit{M}}_{\mathrm{\ensuremath{\perp}}}$ scaling restoration of the dilepton spectra from thermalized matter.