Intermediate mass excess of dilepton production in heavy ion collisions at relativistic energies
Dielectron mass spectra are examined for various nuclear reactions recently measured by the DLS Collaboration. A detailed description is given of all dilepton channels included in the transport model UrQMD 1.0, i.e., Dalitz decays of [Formula Presented] mesons and of the [Formula Presented] resonance, direct decays of vector mesons and [Formula Presented] bremsstrahlung. The microscopic calculations reproduce data for light systems fairly well, but tend to underestimate the data in [Formula Presented] at high energies and in [Formula Presented] at low energies. These conventional sources, however, cannot explain the recently reported enhancement for nucleus-nucleus collisions in the mass region [Formula Presented] Chiral scaling and [Formula Presented] meson broadening in the medium are investigated as a source of this mass excess. They also cannot explain the recent DLS data. © 1998 The American Physical Society.
Ernst, C; Bass, SA; Belkacem, M; Stöcker, H; Greiner, W
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