ReactionO16(π+, pp)14N at 60 MeV: Testing the quasi-deuteron mechanism

A recently proposed phenomenological version of the quasi-deuteron mechanism for pion absorption is applied to low energy pions in flight. We analyze the 60 MeV high resolution data of the reaction ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(${\pi }^{+}$, pp${)}^{14}$N. The distorted wave calculations are successful for the transition to the 3.9 MeV $1^{+}$ state, but fail to explain triple differential cross sections for the transition to the ground state. The strongly anisotropic recoil angle distributions for both states are well accounted for by distortion and polarization effects, the latter being characteristic for transitions with L≠0. Predictions for $2^{+}$ and $3^{+}$ states are given which should allow us to verify our tentative explanation of the recoil angle dependence.