Exciton model description of energy spectra following pion absorption in 40Ca

The spectra of charged particles emitted following the absorption of negative pions at rest in 40Ca are calculated. The pion is assumed to be absorbed on a cluster of two or more nucleons resulting in the emission of a primary particle while the remainder of the cluster equilibrates in the nucleus due to further interactions resulting in the emission of secondary particles. The latter process is described by the exciton case. The proton spectrum is well reproduced assuming absorption on two nucleon clusters only, with a value of R(np/pp)=8+-2 for the ratio of the absorption on a quasi-deuteron to that on a quasi-diproton. The analysis of complex particle spectra indicates pion absorption on heavier clusters also and leads to a phenomenological determination of probabilities for these absorption processes relative to those for two-nucleon clusters. (orig.)