Evidence for a small component of circular polarization in relativistic electron bremsstrahlung

Using a transmission type polarimeter, an asymmetry has been found that can be ascribed to a circularly polarized component in the bremsstrahlung beam of unpolarized relativistic electrons from the Mainz electron linac, in the region of electron energiesE _el between 140 and 400 MeV. The experiment is described in detail. Systematical errors are discussed. For a comparison with electroweak theory, an exact calculation for small photon emission angles (of the order ofm c ²/E _el) is needed.