Energy dependence of hard bremsstrahlung production in proton-proton collisions in the Δ(1232) region

Hard bremsstrahlung production in proton-proton collisions has been studied with the ANKE spectrometer at COSY-Jülich in the energy range of 353-800 MeV by detecting the final proton pair {pp}_s from the pp → {pp}_sγ reaction with very low excitation energy. Differential cross sections were measured at small diproton c.m. angles from 0° to 20° and the average over this angular interval reveals a broad peak at a beam energy around 650 MeV with a FWHM ≈ 220 MeV, suggesting the influence of Δ(1232)N intermediate states. Comparison with deuteron photodisintegration shows that the cross section for diproton production is up to two orders of magnitude smaller, due largely to differences in the selection rules.