Proton-proton bremsstrahlung atTp=730MeV with photon energies up to 300 MeV

The results of new proton-proton bremsstrahlung differential cross section measurements at $T_p=730\mathrm{}$ MeV are presented. The experiment was designed to measure photons of 40-300 MeV at forward angles in coincidence with the scattered and recoil protons. The cross sections rise rapidly when $E_{\gamma }>100\mathrm{}$ MeV, in sharp disagreement with external-emission dominance calculations which predict a smooth and nearly flat spectrum. The model calculations of Tiator et al., which consider the $\Delta \mathrm{}\left(1232\right)\mathrm{}$ resonance in the intermediate state, agree with our results, as does an adjusted soft-photon approximation calculation.