Δ33Dynamics in Pion Double Charge Exchange

The authors calculate effects of direct meson-..delta../sub 33/ interactions on pion double charge exchange to isobaric analog states in /sup 18/O. Virtual ..delta../sub 33/'s in the ground state are shown to contribute negligibly, contrary to recent expectations. On-shell ..delta../sub 33/ interactions can have a large effect through ..pi..+rho exchange, and inclusion of these terms improves agreement with experiment below resonance. Data at the higher energies cannot be explained by a simple combination of sequential pion-nucleon scattering plus direct meson-..delta../sub 33/ terms.