A model for the π-p → π+π-n reaction

Abstract

We describe a model for the π-p → π+π-n reaction that contains one-point, two-point and three-point diagrams with nucleons or deltas in intermediate states. The pieces with N* which do not vanish at threshold are also considered. The model provides a good description of present experiments at low energies with values of the chiral-symmetry-breaking parameter ξ = -0.5-0. The behaviour around threshold is different to extrapolations from present low-energy data used in the literature. At higher energies our results are only about 50% below the most recent experimental data. Inclusion of Δ's and selected N* intermediate-state diagrams helps considerably in improving the agreement with the experimental data as compared to results obtained with a standard model that considers only nucleons as intermediate states. © 1985.