Two-nucleon absorption of π⁺ in ⁴He at T_π⁺=114 and 162 MeV

Differential and integrated cross sections for the reaction ⁴He(π⁺,pp) at T_π=114 and 162 MeV are reported. These are the first results for this reaction using a large solid angle detector covering ≊55% of 4π sr. Directly measured integrated cross sections for absorption on two-nucleon pairs are σ_abs=25.7±1.8 mb at 114 MeV and σ_abs=21.0±1.5 mb at 162 MeV. These cross sections, when corrected by a factor of 1.4 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.