Pion absorption on He3: Absorption amplitude in the Faddeev-quasiparticle scheme

The absorption channel in 3He collisions is investigated. Amplitudes are derived for the pion-induced breakup of the target into both two clusters and three free nucleons. We employ elementary absorption mechanisms of one- and two-body type, which are presently considered to be important for the description of nucleus collisions from the low-energy region up to the region dominated by the resonance. We put the major emphasis on the few-body aspects of the process, such as the three-nucleon dynamics in the final state, and the initial-state breakup of the bound nuclear system in presence of the pion. On the other hand, we neglect pion-nucleus correlations in the initial state, which would entail a complete four-body treatment of the process. For both one- and two-body elementary absorption, the full amplitudes are explicitly represented through quasiparticle (Sturmian) expansions. The entire set of graphs corresponding to the present model is given and discussed.