One of the primary goals of electron scattering experiments is to understand the internal structure of the nucleon, both its static and dynamic properties. Ultimately, electron scattering data will provide benchmarks against which the theoretical predictions of QCD can be compared.

Elastic scattering from the nucleon has been discussed in chapter 22. There are no discrete bound states of the nucleon as there are in nuclei, and thus excited states of the nucleon show up as resonances in particle production processes. This is analogous to the situation with giant resonances in nuclei which lie above particle emission threshold. Nucleon resonances are characterized by strong interaction widths, a typical value for which is given by the time it takes a light signal to travel a pion Compton wavelength, or Γ ≈ ħc/(ħ/mπc) ≈ mπc2 ≈ 135 MeV.

The first inelastic process on the nucleon occurs with the production of the lightest hadron, the pion. The coincidence cross section for the reaction N(e, e′ π)N follows immediately from the general analysis in chapter 13. The angular distribution in the C-M system for arbitrary nucleon helicities is given by Eq. (13.68). If the nucleon target is unpolarized and its final polarization unobserved, the angular distribution reduces to that given in Eqs. (13.71) and (F.9). The analysis of pion electroproduction starting from the covariant, gauge invariant S-matrix and reducing it to the contribution of multipoles leading to states of definite Jπ in the final π−N system is presented in detail in appendix H.