e+e- yields in Pb+Au collisions at 158 AGeV/c: Assessment of baryonic contributions

Abstract

Using a hydrodynamic approach to describe Pb+Au collisions at 158 AGeV/c, we analyze e+e- yields from matter containing baryons in addition to mesons. We employ e+e- production rates from two independent calculations, which differ both in their input physics and in their absolute magnitudes, especially in the mass range where significant enhancements over expected backgrounds exist in the CERES data. Although the presence of baryons leads to significant enhancement of e+e- emission relative to that from mesons-only matter, the calculated results fall below the data in the range 400 < M_ee/MeV < 600, by a factor of 2-3. Since the calculated e+e- spectra are relatively insensitive to the equation of state for initial conditions that fit the observed hadronic spectra, either in-medium modifications of the e+e- sources more significant than so far considered, or the presence of hitherto unidentified additional sources of e+e- is indicated.