Energy dependence of two-nucleon pion absorption on O16

Inclusive O16(π+,p) and exclusive O16(π+,2p) data are presented for 115 MeV and 165 MeV pions. Using a combination of distorted-wave impulse approximation (DWIA) calculations for two-nucleon absorption and phase space simulations for more complicated processes, the data are fit and the total direct two-nucleon absorption cross sections are extracted. These cross sections fall faster with energy than π+d→pp. The DWIA calculations were used to calculate the effects of final state interactions (FSI). After correcting for FSI, the two-nucleon absorption process is found to dominate at 115 MeV, becoming less important as the incident energy increases to 165 MeV. The decrease with energy in the two-nucleon fraction of the total absorption cross section is found to be in remarkably good agreement with theoretical predictions.