Isobar dynamics and pion-nucleus elastic scattering

A new formalism is developed for studying pion-nucleus scattering in a model which takes into account the dynamics of the (3,3) pion-nucleon resonance, or Δ isobar. This treatment is used to calculate π+ elastic scattering from 16O, 40Ca, 48Ca and 208Pb at energies from 114 to 240 MeV. Some results for π- elastic scattering are also given. From fits to π+ scattering data it is found that the Δ-nucleus interaction is well described by a spherical local complex potential proportional to the nuclear density. The central strength of this potential depends on energy but not on nuclear mass number. Some difficulties in determining the parameters of this potential from elastic scattering are discussed. (orig.)