Dominance of the two-nucleon mechanism in 16O( pi +,pp) at 115 MeV.

Singles {sup 16}O({pi}{sup +},{ital p}) and coincidence {sup 16}O({pi}{sup +},2{ital p}){sup 14}N measurements have been made at {ital T}{sub {pi}}=115 MeV over an extended range of the phase space of the two final-state protons. The coincidence measurements have a missing-mass resolution of 4 MeV. The direct two-nucleon absorption cross section extracted from the data is 58{plus minus}8 mb. After corrections for final-state interactions, it was found that the two-nucleon {pi}{sup +}+{ital np}{r arrow}{ital pp} process accounts for about 76% of the total absorption cross section, and thus is the dominant absorption mechanism. Evidence for absorption on {ital s}-{ital p} pairs is seen as a broad bump near 32 MeV of excitation. At backward angles the inclusive {sup 16}O({pi}{sup +},{ital p}) spectra show a distinct absorption peak, an important feature not previously observed. Comparisons of distorted wave impulse approximation calculations to both the coincidence data and inclusive data are presented.