Di-electron production from vector mesons with medium modifications in heavy ion collisions

Abstract

We reproduce the di-electron spectra in the low and intermediate mass regions in most central Au+Au collisions by the STAR Collaboration incorporation of the STAR detector acceptance. We also compare our results with PHENIX data constrained by the PHENIX acceptance. We include the medium modifications of vector mesons from scatterings of vector mesons by mesons and baryons in the thermal medium. The freezeout contributions from vector mesons are also taken into account. The space-time evolution is described by a 2+1 dimensional ideal hydrodynamic model. The backgrounds from semi-leptonic decays of charm hadrons are simulated by the PYTHIA event generator and corrected by the nuclear modification factor of electrons from charm decays. It is difficult to extract the thermal contributions from those from charm decays in the invariant mass spectra alone and in the current detector acceptances. Other observables such as transverse momenta and collective flows may provide additional tools to tag these sources.

Dielectron Mass Spectra fromAu+AuCollisions atsNN=200 <

“…Compared to our data in the mass region below 1 GeV=c 2 , both models describe the observed dielectron excess reasonably well within uncertainties. Other theoretical model calculations can also reproduce the dielectron excess at low mass in our measurement [34,35]. Our measurements disfavor a pure vacuum ρ spectrum for the excess dielectrons (χ 2 =NDF ¼ 26=8, where NDF is the number of degrees of freedom, in 0.3-1 GeV=c 2 ) .…”