The Sherman function and its radiative corrections for the elastic scattering of positrons from spin-zero nuclei

The beam-normal spin asymmetry S from the scattering of spin-polarized positrons is estimated by means of the phase-shift analysis. A nonperturbative inclusion of quantum electrodynamical (QED) effects leads to modifications of S in the percent region for collision energies above 20 MeV. Second-order Born predictions for the dispersive corrections are also made by considering the dominant low-lying nuclear excitations. As examples, the 12C and 208Pb target nuclei are studied, predominantly for collision energies up to the pion production threshold. The comparison with results from electron scattering shows that the influence of the Coulomb distortion is, in contrast to 12C, very significant for 208Pb.