The equivalent polarised-photon approximation

The equivalent photon approximation is studied for the case where the scattered electron is detected. The equivalent photon is then polarised. The region of validity is found to depend on the virtual photon scattering angle, rather than on the electron scattering angle, and this distinction is important. A discrepancy concerning the dependence on beam energy of the total cross section for $\text{e}\text{e}\text{?}\text{→}\text{e}\text{e}\text{?}\text{+}$ hadrons which was noted by Bonneau et al. is resolved.