Transverse-flow effects in dilepton emission

Abstract
Dilepton emission from expanding QCD matter formed in ultrarelativistic nuclear collisions is computed. The energy density and the velocity field of the expanding matter are computed numerically with a (1+3)-dimensional numerical code which assumes cylindrical invariance in the transverse and boost invariance in the longitudinal direction. Effects of transverse flow are studied and shown to be important in the region of pair mass M≲1.2 GeV. The existence of transverse flow results in the persistent appearance of the ρ peak in the M distribution at fixed transverse mass MT for large MT. The initial temperature Ti and the thermalization time τi of the hydrodynamical flow are related to the associated pion multiplicity dN/dy and the dilepton emission rate at M>1.5 GeV.