Three-nucleon pion absorption in carbon.

Abstract

We have performed an experiment in which we have detected three protons in coincidence, following the absorption of positive pions in carbon. Data were collected with twelve plastic scintillator detectors, covering a fairly large region of the available phase space, at three incident pion kinetic energies: ${T}_{\ensuremath{\pi}}$=130, 180, and 228 MeV. Comparisons are made with phase space calculations which simulate quasifree three-nucleon and four-nucleon absorption mechanisms. The first of these provides an excellent description of the bulk of the data. Some of the observed events appear to come from quasideuteron absorption, followed by a final-state interaction of one of the outgoing protons. There is no evidence for absorption mechanisms involving more than three nucleons. Estimates are made for the contributions of the three-nucleon absorption mechanisms to the total pion absorption cross section. These are relatively small.