Anomalously low cross section inC13(γ,π−)Ng.s.13

Differential cross sections for the reaction ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$($\gamma$,${\pi }^{-}$)${}_{}{}^{13}{}_{}{}^{}\mathrm{N}_{\mathrm{g}.\mathrm{s}.\mathrm{}}^{}{}_{}{}^{}$ were measured at 90° (lab) for three pion energies: 17, 29, and 42 MeV. The experimental cross sections are anomalously low compared with distorted wave impulse approximation calculations and contrary to the predicted enhancement due to pion condensation precursor effect.