Dielectron Mass Spectra from Au plus Au Collisions at root s(NN)=200 Ge V

We report the STAR measurements of dielectron (e(+)e(-)) production at midrapidity (vertical bar y(ee)vertical bar < 1) in Au + Au collisions at root s(NN) = 200 GeV. The measurements are evaluated in different invariant mass regions with a focus on 0.30-0.76 (rho-like), 0.76-0.80 (omega-like), and 0.98-1.05 (phi-like) GeV/c(2). The spectrum in the omega-like and phi-like regions can be well described by the hadronic cocktail simulation. In the rho-like region, however, the vacuum rho spectral function cannot describe the shape of the dielectron excess. In this range, an enhancement of 1.77 +/- 0.11(stat) +/- 0.24(syst) +/- 0.33(cocktail) is determined with respect to the hadronic cocktail simulation that excludes the rho meson. The excess yield in the rho-like region increases with the number of collision participants faster than the omega and phi yields. Theoretical models with broadened rho contributions through interactions with constituents in the hot QCD medium provide a consistent description of the dilepton mass spectra for the measurement presented here and the earlier data at the Super Proton Synchrotron energies.