The 3He(p,π+)4He reaction near threshold

We apply a recently developed microscopic model of nuclear pion production to the 3He(p,π+)4He reaction at Tp=200 MeV and show the approximate equivalence for this reaction of a one-nucleon mechanism (ONM) calculation with full proton and pion distortions to a more microscopic calculation involving the coherent sum of the ONM amplitude with proton and nonresonant pion distorted waves and the pion-exchange projectile-emission part of the two-nucleon mechanism amplitude with proton and full pion distortions. A full microscopic calculation including target-emission and p-meson exchange contributions describes qualitatively the shapes of the differential cross section and analyzing power angular distributions but underestimates the magnitude of the measured cross sections. The sensitivity of the calculations to D-state admixtures in the bound-state wave functions is shown to be small. (orig.)