Dilepton production in nucleon-nucleon reactions with and without hadronic inelasticities.

We calculate elementary proton-proton and neutron-proton bremsstrahlung and their contribution to the e+e− invariant mass distribution. At 4.9 GeV, the proton-proton contribution is larger than neutron-proton, but it is small compared to recent data. We then make a first calculation of bremsstrahlung in nucleon-nucleon reactions with multi-hadron final states. Again at 4.9 GeV, the many-body bremsstrahlung is larger than simple nucleon-nucleon bremsstrahlung by more than an order of magnitude in the low-mass region. When the bremsstrahlung contributions are summed with Dalitz decay of the η, radiative decay of the ∆ and from two-pion annihilation, the result matches recent high statistics proton-proton data from the Dilepton Spectrometer collaboration. internet: [email protected]. internet: [email protected] Permanent address: Physics Department, McGill University, 3600 University Street, Montréal QC, Canada H3A 2T8 Present address: Physics Department, McGill University, 3600 University Street, Montréal QC, Canada H3A 2T8; After 1 September 1993: Michigan State University, East Lansing, Michigan 48824