Pion absorption reaction on 2H and 3He in the Δ-isobar region

Abstract

By using Faddeev equations the absorption of π + on 3He in the Δ-isobar region is investigated with the final state three-nucleon interaction. We calculated the NN - NΔ t-matrix and πN → Δ vertex from a phenomenological model for NN and πd reactions. In case of neglecting the initial pion scattering effects the theoretically predicted peaks of the pion absorption cross sections for 2H and 3He occur at too high an energy with respect to the data. It is shown that the final state three-nucleon interactions have a negligible effect on the magnitude and the shift of the peak position. By a small modification of the Δ bare mass and the πNΔ coupling strength the peak positions of the absorption cross sections of 2H and 3He are simultaneously brought to the correct peak position. The Dalitz plots of the outgoing three protons are shown and compared to the recent PSI measurements using kinematics cuts which almost eliminate the contribution from quasi free pion absorption.