Dilepton production in proton-proton and quasifree proton-neutron reactions at 1.25 GeV

Understand

We investigate the pp --> pp e+e- and quasifree pn --> pn e+e- reactions within an effective Lagrangian model at the laboratory kinetic energy of 1.25 GeV for which experimental data have recently been reported by the HADES Collaboration.

• The model uses a meson-exchange approximation to describe the initial nucleon-nucleon (NN) scattering.
• Contributions to the reaction amplitudes are included from the NN bremsstrahlung as well as from the excitation, propagation and radiative decay of the Delta(1230) isobar state.
• It is found that the HADES data on the e+e- invariant mass distribution in the pp --> pp e+e- reaction are reproduced excellently by our model where the Delta isobar term dominates the spectrum.