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

Differential and integrated cross sections for the reaction $^{4}\mathrm{He}$(${\mathrm{\ensuremath{\pi}}}^{+}$,pp) at ${\mathit{T}}_{\mathrm{\ensuremath{\pi}}}$=114 and 162 MeV are reported. These are the first results for this reaction using a large solid angle detector covering \ensuremath{\approxeq}55% of 4\ensuremath{\pi} sr. Directly measured integrated cross sections for absorption on two-nucleon pairs are ${\mathrm{\ensuremath{\sigma}}}_{\mathrm{abs}}$=25.7\ifmmode\pm\else\textpm\fi{}1.8 mb at 114 MeV and ${\mathrm{\ensuremath{\sigma}}}_{\mathrm{abs}}$=21.0\ifmmode\pm\else\textpm\fi{}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.