2-NUCLEON ABSORPTION OF PI+ IN HE-4 AT T-PI+ = 114 AND 162 MEV

Differential and integrated cross sections for the reaction He-4(pi+, pp) at T(pi)=114 and 162 MeV are reported. These are the first results for this reaction using a large solid angle detector covering almost-equal-to 55% of 4(pi) sr. Directly measured integrated cross sections for absorption on two-nucleon pairs are sigma(abs) = 25.7+/-1.8 mb at 114 MeV and sigma(abs) = 21.0+/-1.5 mb at 162 MeV. These cross sections, when corrected by a factor of 1.4 for final-state interaction effects, account for about 50% of the total absorption cross section for all final state reaction channels at both energies, The data are compared with Monte Carlo simulations of the reaction process using a quasideuteron absorption model for the two-nucleon absorption process in a plane wave impulse approximation. The consequences for the extraction of the two-nucleon absorption cross section by imposing different conditions on the data are explored.