Di-electron bremsstrahlung in intermediate-energy pn and Dp collisions

Invariant mass spectra of di-electrons stemming from bremsstrahlung processes are calculated in a covariant diagrammatical approach for the exclusive reaction Dp→pspnpe+e− with detection of a forward spectator proton, psp. We employ an effective nucleon–meson theory for parameterizing the subreaction np→npe+e− and, within the Bethe–Salpeter formalism, derive a factorization of the cross section in the form dσDp→pspnpe+e−/dM=dσnp→npe+e−/dM× kinematical factor related solely to the deuteron (M is the e+e− invariant mass). The effective nucleon–meson interactions, including the exchange mesons π, σ, ω and ρ as well as excitation and radiative decay of Δ(1232), have been adjusted to the process pp→ppe+e− at energies below the vector meson production threshold. At higher energies, contributions from ω and ρ meson excitations are analyzed in both, NN and Dp collisions. A relation to two-step models is discussed. Subthreshold di-electron production in Dp collisions at low spectator momenta is investigated as well. Calculations have been performed for kinematical conditions envisaged for forthcoming experiments at HADES.