Dielectron measurement in p+p interactions at 3.5 GeV with HADES

Fig. 1 shows the comparison of the measured dielectron spectra to simulations performed with the PLUTO event generator [2] inside the geometrical acceptance of HADES. The low-mass region of the spectra is dominated by Dalitz decays of π, η, ω as well as by the Dalitz decay of the ∆(1232) resonance. The evident peak around the pole mass of the ω meson, with width of 17 ± 2 MeV, corresponds to its direct decay into e+e− pairs. In the simulation pions are produced through nucleon resonances, as described in [3], while for all other particles, except ∆, constant matrix elements, i.e. phase-space production, are used. The ∆ isobar production is parametrized according to [4] while its production cross section of 17mb is taken from the PYTHIA event generator. For the differential Daltitz decay rate of the baryon resonances the calcu-