Binding and pauli principle corrections in subthreshold pion-nucleus scattering

In this investigation I develop a three-body model for the single scattering optical potential in which the nucleon binding and the Pauli principle are accounted for. A unitarity pole approximation is used for the nucleon-core interaction. Calculations are presented for the π−⁴He elastic scattering cross sections at energies below the inelastic threshold and for the real part of the π−⁴He scattering length by solving the three-body equations. Off-shell kinematics and the Pauli principle are carefully taken into account.

The binding correction and the Pauli principle correction each have an important effect on the differential cross sections and the scattering length. However, large cancellations occur between these two effects. I find an increase in the π−⁴He scattering length by 100%; an increase in the cross sections by 20–30% and shift of the minimum in π−⁴He scattering to forward angles by 10°.