Differential cross section for proton-proton bremsstrahlung at 1.38 GeV/c

We present the differential cross section for proton-proton bremsstrahlung at an incident beam momentum of 1.38 GeV/c (730 MeV). The measurements are made with an overconstrained detection system to reliably exclude all $\mathrm{pp}\to \mathrm{pp}{\pi }^0$ events. We have obtained differential cross sections at 16 photon angles at photon energies up to 200 MeV for protons scattered at 50° (lab). For each of the photon angles, $\frac{d^5\sigma }{d{\Omega }_{p}d{\Omega }_{\gamma }d{E}_{\gamma }}$ decreases smoothly with increasing photon energy up to $E_{\gamma }\left(\mathrm{lab}\right)\simeq 80$ MeV. Above this photon energy the cross sections rise again. Our results are compared with the soft photon approximation and the external emission dominance calculations. The soft photon approximation describes most spectra fairly well up to $E_{\gamma }\simeq 100$ MeV and external emission dominance up to $E_{\gamma }\simeq 60$ MeV (lab), but both predict cross sections which are too small at the highest photon energies.