PHENIX results on low-mass dileptons in Au + Au collisions with the Hadron Blind Detector

Abstract

We present e+e− continuum measurement in Au+Au collisions at sNN=200 GeV from the RHIC 2010 run with the Hadron Blind Detector upgrade of PHENIX. The measurement reaches a high purity of the electron sample of ≥ 95% at all centralities and provides an excellent qualitative and quantitative understanding of the background. The e+e− invariant yields show an enhancement in the low-mass region (mee=0.30−0.76 GeV/c2) compared to the expectations from hadronic sources, but not as large as the one previously reported by PHENIX. The observed excess is well reproduced by models incorporating the broadening of the ρ meson due to scattering off baryons in the hot hadronic gas. The measured invariant yields in the intermediate-mass region (mee=1.2−2.8 GeV/c2) leave room for additional sources when compared to the cocktail dominated by the semileptonic decays of heavy flavor mesons.