ReactionNi58(π+,pp) atTπ+=160 MeV

The reaction ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$(${\mathrm{\pi }}^{+}$,pp) was studied with good energy resolution for an incident pion energy of 160 MeV. The angular correlation of the outgoing protons was measured for ${\mathrm{\theta }}_{\mathrm{lab}}$=30°, 75°, and 130°. From these angular correlations the contribution from direct two-nucleon absorption was extracted. A Monte Carlo calculation modeling the absorption process in terms of initial-state scattering of the pion before absorption, two-nucleon absorption, and final-state scattering of the outgoing nucleons is compared to the data. We conclude that within this framework the two-nucleon mechanism can account for less than half of the total absorption cross section in ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$. We report results for the low-energy coincidence proton spectra (down to 5 MeV) which suggest that most of these protons come from evaporation. Angular correlation data for the reaction ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$(${\mathrm{\pi }}^{\mathrm{-}}$,pp) are also presented.