We calculate the total cross section for the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}(\gamma ,{\pi }^{-}){}_{}{}^{12}{}_{}{}^{}\mathrm{N}_{\mathrm{g}.\mathrm{s}.\mathrm{}}^{}{}_{}{}^{}$ and study its energy dependence in the threshold region. Contrary to previous theoretical analyses, we find agreement between theory and experiment using a $\overrightarrow{\sigma }·\overrightarrow{\epsilon }$ interaction. Our results depend strongly on the inclusion of all pion partial waves and a correct treatment of the isospin dependent terms in the pion-nucleus optical potential.

[NUCLEAR REACTIONS ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}(\gamma ,{\pi }^{-}){}_{}{}^{12}{}_{}{}^{}\mathrm{N}_{\mathrm{g}.\mathrm{s}.\mathrm{}}^{}{}_{}{}^{}$; photon lab. energy 0-10 MeV above threshold; realistic pion optical potential; shell model wave functions; $\overrightarrow{\sigma }·\overrightarrow{\epsilon }$ interaction. Calculated total cross section.]

• Received 12 September 1977

DOI:https://doi.org/10.1103/PhysRevC.17.702