Delta-hole approach to pion double charge exchange

We present a semi-microscopic model for the double charge exchange (DCX) reaction (π+, π-) to the ground state of the final nucleus at medium and low energies. We separate the DCX amplitude into a sequential and a non-sequential part, with pions distorted by the full Δ-hole optical potential and medium corrections to the resonant π--N amplitude taken into account partly microscopically (Δ propagation, binding, and Pauli blocking) and partly phenomenologically (spreading potential). In the non-sequential part of the amplitude charge exchange takes place between the Δ and a nucleon via a phenomenological Δ--N interaction. We find that the sequential amplitude alone provides an adequate description of the reaction at low energies (where it proceeds predominantly via non-analog intermediate states). At higher energies the short-range Δ--N interaction begins to play a more important role and the non-sequential amplitude interferes delicately with the sequential one. We are able to describe the DCX reaction well for 14C at all energies, for 16O up to resonance and for 18O at 50 MeV, but we are not able to reproduce the energy and angular dependence of the 18O cross-section in the medium energy region. Copyright 1987 Academic Press, Inc