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 multihadron 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 {Δ} and from two-pion annihilation, the result matches recent high statistics proton-proton data from the Dilepton Spectrometer collaboration.