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

Using a hydrodynamic approach to describe Pb + Au collisions at 158 A GeV/c , we analyze e(+)e(-) yields from matter containing baryons in addition to mesons. We employ e(+)e(-) production rates from two independent calculatio ns, which differ both in their input physics and in their absolute magnitud es, especially in the mass range where significant enhancements over expect ed backgrounds exist in the CERES data. Although the presence of baryons le ads to significant enhancement of e(+)e(-) emission relative to that from m esons-only matter, the calculated results fall below the data in the range 400 < Me+e-/MeV < 600, by a factor of 2-3. Since the calculated e(+)e(-) sp ectra are relatively insensitive to the equation of state for initial condi tions that fit the observed hadronic spectra, either in-medium modification s of the e(+)e(-) sources more significant than so far considered, or the p resence of hitherto udidentified additional sources of e(+)e(-) is indicate d. (C) 1999 Elsevier Science B.V. All rights reserved.