Multi-nucleon pion absorption in the 4He(π+, ppp)n reaction

Three-proton emission cross sections for the 4He(π+, ppp)n reaction were measured at Tsub(π+)=165 MeV over a wide angular range in a kinematically complete experiment. The momentum distribution of the undetected neutron and angular correlations have been compared with three- and four-body phase space Monte Carlo calculations. The results indicate that most of three-proton coincidences result from three nucleon absorption. The total three-nucleon absorption cross section is estimated to be σ3N=4.5±1.0 mb from phase-space integration. This cross section does not account for the discrepancy between total absorption cross sections and two-nucleon absorption cross sections. (orig.)