Abstract
Pion photoproduction up to 770 MeV photon laboratory energy is described by a manifestly covariant wave equation, which includes a treatment of the final state πN interactions consistent with the covariant, unitary, resonance model of πN scattering previously developed. The kernel of the equation includes nucleon (N), Roper (), delta (Δ), and poles and their crossed poles, as well as π, ρ, and ω exchange terms. The Kroll-Rudermann term and other interaction currents ensure that the model is exactly gauge invariant to all orders in the strong coupling . The threshold value of the amplitude is in good agreement with recent estimates obtained from chiral perturbation theory. Elastic unitarity to first order in the charge e (Watson theorem) is maintained up to the two-pion production threshold. The complete development of this model, which gives a good fit to all L≤2 multiples up to 770 MeV, is presented. © 1996 The American Physical Society.
- Received 23 March 1995
DOI:https://doi.org/10.1103/PhysRevC.53.2422
©1996 American Physical Society