Pi - absorption on the diproton in 3He.

Abstract

Absorption of negative pions on $^{1}$${\mathit{S}}_{0}$ proton pairs is studied in a model which treats the two nucleon final-state interactions (including isobar components, which simulate pion p-wave scattering) in an exact way, but leaves the third nucleon an inactive spectator. Pion s-wave rescattering is included by a phenomenological Hamiltonian. Otherwise the initial-state pions are considered undistorted. The influence of different proton pair wave functions, final-state interactions, and pion-nucleon vertex forms is studied. The experimentally observed asymmetry of the cross section about 90\ifmmode^\circ\else\textdegree\fi{} is obtained only if a Galilean-invariant pion absorption operator is used. The final-state interaction is particularly important in the tensor coupled $^{3}$${\mathit{S}}_{1\mathrm{\ensuremath{-}}}^{3}$${\mathit{D}}_{1}$ states, with the final $^{3}$${\mathit{D}}_{1}$ state emerging as the dominant one. The normal polarization of outcoming protons is similar to the analyzing power in the reaction p\ensuremath{\rightarrow}+n\ensuremath{\rightarrow}(pp${)}_{\mathit{S}\mathrm{wave}}$+${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$ and is very insensitive on any details of the dynamical input. Also the polarization correlation coefficients show relatively little dependence on the model being rather constrained by kinematics.