On the reaction $ep \to ep \gamma$

Abstract

We have studied the reaction $ep \to ep \gamma$ in the kinematics corresponding to electron scattering at small angles and photon scattering at large angles, where proton bremsstrahlung dominates. The analysis is based on the direct evaluation method of the matrix elements in the so-called diagonal spin basis. The results of numerical calculations for electron beam energy $E_{e}=200 MeV$ in the above kinematics show that the relative contribution of the Bethe-Heitler and interference terms to the reaction cross section is less than 10 %, and the cross section for the reaction $ep \to ep \gamma$ is quite sensitive to the proton polarizability. Owing to the factorization of the squared electric and magnetic form factors of the proton, a compact expression has been obtained for the differential cross section of the Bethe-Heitler emission of a linearly polarized photon by an electron, taking into account the proton recoil and form factors. A covariant expression has been obtained for the lepton tensor in which contributions of states with transverse and longitudinal polarizations of the virtual photon are separated.