R. R. Johnson

Multinucleon pion absorption in theHe4(π+,ppp)nreaction

Three-proton emission cross sections for the {sup 4}He({pi}{sup +},{ital ppp}){ital n} reaction were measured at an incident pion kinetic energy of {ital T}{sub {pi}}{sup +}=165 MeV over a wide angular range in a kinematically complete experiment. Angular correlations, missing momentum distributions, and energy spectra are compared with three- and four-body phase-space Monte Carlo calculations. The results provide strong evidence that most of the three-proton coincidences result from three-nucleon absorption. From phase-space integration the total three-nucleon absorption cross section is estimated to be {sigma}{sup 3{ital N}}=4.8{plus minus}1.0 mb. The cross section involving four nucleons is small and is estimated to be {sigma}{sup 4{ital N}}{lt}2 mb. On the scale of the total absorption cross section in {sup 4}He, multinucleon pion absorption seems to represent only a small fraction.

Measurement of the /sup 16/O(. pi. /sup +/,. pi. /sup +/. pi. /sup -/) reaction at T/sub. pi. //sub =/ = 280 MeV

Results from a coincidence measurement of the /sup 16/O(..pi../sup +/,..pi../sup +/..pi../sup -/) reaction at T/sub ..pi..//sub =/ = 280 MeV are reported, the first of this class. The energy- and angular-integrated cross section was found to be 2950 +- 450 ..mu..b and is compared with theoretical predictions. Low-energy positive-pion intensities are found to be much higher than those yielded by a four-body phase-space calculation.