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

Abstract

Invariant mass spectra of di-electrons stemming from bremsstrahlung processes are calculated in a covariant diagrammatical approach for the exclusive reaction D p → p sp n p e + e − with detection of a forward spectator proton, p sp . We employ an effective nucleon–meson theory for parameterizing the subreaction n p → n p e + e − and, within the Bethe–Salpeter formalism, derive a factorization of the cross section in the form d σ D p → p sp n p e + e − / d M = d σ n p → n p e + e − / d M × 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 p p → p p e + 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.