Key points are not available for this paper at this time.
The close relationship between photopion and electropion production from protons allows an unambiguous first estimate (the standard value) for the ratio of these cross sections, based on assumptions very close to those of the Weizs\"acker-Williams method. Deviations of the ratio from this estimate arise from pion production by the longitudinal components of the field of the scattered electron and from the variation of the off-diagonal transverse excitations from their diagonal photoproduction values. The dependence of these deviations on the physical processes contributing to the electromagnetic excitation of pions is discussed in terms of matrix elements specified in the pion-nucleon center-of-mass system, both for various phenomenological contributions and for specific meson theories. The experimental values reported are interpreted as an indication of the smallness of longitudinal production, in qualitative accord with the fixed source theory. These features may also be investigated by study of the energy spectrum of inelastically scattered electrons and of the azimuthal variation of pion production relative to the scattering plane, which are also discussed here.
Dalitz et al. (Fri,) studied this question.