Measurement of radiative pion-proton scattering at backward photon angles

Abstract

We have measured the differential cross sections for ${\pi }^{+}p$ and ${\pi }^{-}p$ radiative scattering (${\pi }^{\pm }p\to {\pi }^{\pm }p\gamma$) at an incident kinetic energy of 298 MeV with photons produced at very large angles to the incident and scattered particles. The measured photon spectrum extended to 120 MeV. For photon energies below 30 MeV, the results are in agreement with the conventional soft-photon formalism. In the hard-photon region the data fail to reflect the $\Delta \mathrm{}\left(1236\right)\mathrm{}$ resonance in the final state, and are in substantial disagreement with existing theoretical models.