PHOTOPRODUCTION OF PIONS FROM THE NUCLEON

The basic features of relativistic quantum mechanics §are outlined as well as the Bakamjian Thomas §procedure for constructing quantum mechanical models §that satisfy the requirements of special relativity. §The general structure of the mass operator obtained §in a Bakamjian Thomas construction is given. The §procedure for constructing quantum mechanical states §that transform correctly under the action of the §Poincaré group is presented. Both proper Poincaré §transformations and space inversions are considered. §A derivation is given of the general structure of a §Poincaré and gauge invariant mass operator that §couples baryon states to photon baryon states and §meson-baryon states to photon baryon states. The §general isospin structure of such a mass operator is §also developed. The Lippmann Schwinger equations §that the mass operator gives rise to are presented §and the relation of their solutions to multipole §amplitudes is obtained. Various formulas for cross §sections are derived. Okubo s method and effective §Lagrangians are used to derive a model for a mass §operator that describes the photoproduction of pions §from the nucleon.