Final-state effects in the (π^-, 2N) reaction

The (π^-, 2N) reaction is studied theoretically with the specific cases of ¹⁶O(π^-, 2n)¹⁴N and ¹⁶O(π^-, pn)¹⁴C as calculational examples. The aim of the work is to investigate the sensitivity of the reaction to various theoretical mechanisms - especially to final-state interactions - and to confront the results with the experimental data that have become available in recent years. The final-state problem is treated including the nucleon-nucleon and nucleon-nucleus interactions simultaneously with a realistic, local and complex optical potential for the latter. The initial state includes a correlation function, and the absorption mechanism is generally taken to be the direct absorption mode, though we also study the π- and ρ-rescattering contributions to the absorption operator using a Δ-isobar intermediate-state mechanism. Angular correlations and energy distributions are found to be in reasonable agreement with experiment though the ratio of nn to np emission remains problematic.