Dilepton Production In Relativistic Heavy Ion Collisions

We investigated the dilepton production in the low and intermediate mass region in central collisions at the RHIC energy. The space-time evolution is described by a2+1dimensional ideal hydrodynamic model. The parameters in the hydrodynamic mod-el are constrained by the experimental data for long life hadrons. We calculated the dilepton emission rate from qq annihilation in the QGP phase, in-medium vector meson decays in the hadronic phase and freeze out vector meson decays at the thermal freeze-out, respectively. Using the hadronic many body theory and the empirical scattering amplitude method, we include medium modifications of vector mesons from scatter-ings by mesons and baryons in a thermal medium. The backgrounds from semileptonic decays of charm hadrons are simulated by the PYTHIA event generator and correct-ed by the nuclear modification factor of electrons from charm decays. With the STAR (PHENIX) acceptance, we compute the di-electron spectra in most central collision-s and compare them with the STAR preliminary (PHENIX) data at0-10%centrality. It is difficult to extract thermal contributions from that of charm decays in the current detector acceptances.The properties of the transverse flow of long life hadrons from hydrodynamic sim-ulation are discussed in a simple model. We also investigated the transverse flow of dileptons in minimum bias collisions at the RHIC energy. We calculated the elliptic flow of dileptons from the QGP phase, the hadronic phase and vector meson decays at thermal freeze-out, respectively. With the fraction of each sources corrected by the STAR acceptance, we predict the mass differential elliptic flow of di-electrons in mini-mum bias collisions. To compare with the in-medium vector meson decays, the dilepton production from the QGP phase and charm hadron decays decreases with the decreas-ing initial energy density (with the increasing centrality, in other words). We found that even the thermal elliptic flow decreases in the invariant mass region above the free φ meson mass, the total elliptic flow increases in such mass region due to the significant contribution from the charm hadrons decays.