Exclusive quasi-deuteron absorption of pions in ' 0 and ' 0 at 116 MeV

The reaction ' O(v+, 2p)' N was measured at T =116MeV with an excitation energy resolution between 1.6 and 2.5 MeV with one proton angle fixed at 50' and for a wide range of the second angle. Proton angular correlations, energy sharing distributions, and recoil momentum distributions for four strongly populated states are consistent with a model of pion absorption on quasi-deuteron pairs with angular momentum transfer to the recoil nucleus of L =0 (3.9 MeV state), L =2 (7.0 and 11.0 MeV states), or a mixture of L =0 and L =2 (ground state). Integration of the measured absorption cross section over angle and up to 20 MeV of excitation shows that 19+4% of the total absorption cross section can be found in two-proton final states near quasifree kinematics, with substantial additional two-nucleon strength between 20 and roughly 50 MeV of excitation. With estimated corrections for final-state interactions, about half of the absorption cross section below 20 MeV excitation proceeds via the direct quasifree mpn ~pp process. Absorption leading to the T = 1 state at 2.3 MeV is & 5% as strong as absorption to the T =0 ground state. The "O(m+, 2p)' N reaction was measured under the same kinematic conditions. States of less than 0.4 MeV excitation, which correspond to absorption on nucleons in different shells, account for at least 6. 1+0.6% of the estimated two-nucleon absorption cross section below 20 MeV excitation; no unexpected suppression of cross-shell absorption was found.