Delta resonance and nonlocal effects in pion photoproduction from nuclei

The photoproduction of charged pions from light nuclei is investigated in a distorted wave impulse approximation carried out in momentum space. This permits a straightforward inclusion of nonlocal terms in the pion production operator such as that of Blomqvist and Laget. The interaction of the outgoing pion with the residual nuclear state is described by the optical potential of Stricker, McManus, and Carr. The cross section for pion production from $p$-shell nuclei is decomposed into partial cross sections labeled by transition angular momenta and spin which are almost independent of nuclear structure. Using the reaction $^{13}\mathrm{C}(\ensuremath{\gamma},{\ensuremath{\pi}}^{\ensuremath{-}})^{13}\mathrm{N}_{\mathrm{g}.\mathrm{s}.}$, the effects of the delta isobar in the production operator on these partial cross sections is investigated. The same reaction is used to demonstrate the inadequacy of local coordinate space analyses.

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