One-nucleon knockout by pions and deltas

We present the first quantitative study of the (π,π’N) coincidence reaction within the Δ-hole model and compare our results to recent Swiss Institute for Nuclear Research (SIN) and LAMPF data for ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ near 240 MeV. A modified distorted-wave impulse approximation (DWIA), including medium corrections to the Δ propagator and containing no free parameters, reproduces the leading (${\pi }^{+}$,${\pi }^{+}$p) channel for p-shell knockout satisfactorily, provided we use shell-model spectroscopic factors. The weak (${\pi }^{\mathrm{-}}$,${\pi }^{\mathrm{-}}$p) and (${\pi }^{+}$,${\pi }^0$p) channels are found to be sensitive to interference effects between the DWIA mechanism and knockout induced by ΔN collisions. This latter two-step process is also calculated microscopically, using a simple form for the Δ-N interaction guided by pion absorption. Our model qualitatively confirms earlier estimates, but cannot reproduce the isospin ratios over the whole kinematical range. In particular, it systematically underestimates the charge-exchange cross sections by 30%.