CERES results on low-mass electron pair production in Pb-Au collisions

The CERES/NA45 collaboration measured, at the CERN SPS, low-mass electron pair production in Pb-Au collisions at 158AGeV/c incident momentum. In this paper we present an analysis of the data taken during the SPS Pb-beam period in the fall of 1995. The results confirm previous findings of CERES showing that the pair production in the mass range 0.2<mee<1.5GeV/c2, when scaled to the ion case with the event multiplicity, is enhanced over the expected yield from the known hadronic sources in pp collisions. A comparison of the results for different multiplicity bins indicates that the excess increases faster than linearly with charged-particle multiplicity. We also present the transverse-momentum distributions of the observed pairs