PION ABSORPTION BY HE-3 AT THE DELTA-RESONANCE ENERGY

Pion absorption by 3He was studied at T-pi = 165 MeV in a kinematically complete experiment. The cross section for absorption on a (pn) pair of nucleons, sigma-pn (pi+), was found to be 17.0 +/- 2.6 mb; that for absorption on a (pp) pair, sigma-pp (pi-), 0.91 +/- 0.20 mb. The angular distribution in the pi-NN center-of-mass system for sigma-pn (pi+) resembles that for the pi+ +d-->p + p reaction while the angular distribution for sigma-pp (pi-) is strongly backward peaked. Evidence that a significant fraction of the absorptions involves all three target nucleons is seen in the angular correlation between the two detected nucleons as well as in the momentum distribution of the unobserved nucleon. For pi+ and pi- absorption, the three-body cross sections were found to be 9.6 +/- 2.1 and 4.2 +/- 01.2 mb, respectively. Neither initial- nor final-state interactions appear to be major contributors to the observed three-body absorption, though initial-state interactions may be contributing to the enhancement of the three-body pi+ absorption at the DELTA resonance.