C12(γ,π−)Ng.s.12near threshold

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.