Virtual pion scattering

We explore coherent pion production in (3He,3Hπ+) and (p,nπ+) reactions as effective virtual pion scattering, in calculations of cross sections to the ground state and low-lying excitations of the target nucleus. Our coupled-channel model includes a source term emulating a virtual-pion beam and an optical potential for the interaction of the pion in the medium. We demonstrate that the landmark lowering of the peak in the energy-transfer spectra is entirely determined by the rescattering of the pion, and that its low-energy wing is sensitive to the pion-nucleon s-wave amplitude including its off-shell behavior.