Systematics of the low-energy pionic double charge exchange in nuclei

The experimental results for the $({\ensuremath{\pi}}^{+},{\ensuremath{\pi}}^{\ensuremath{-}})$ reaction on nuclei obtained in recent years reveal clear systematic features of this reaction. New data on ${}^{7}\mathrm{Li},$ ${}^{12}\mathrm{C},$ ${}^{16}\mathrm{O},$ and ${}^{56}\mathrm{Fe}$ supplementing the existing data base are presented. The data on ${}^{12}\mathrm{C}$ are partly at variance with previous results. The dependence of the cross sections on incident energy, scattering angle, and on the target mass is discussed for transitions leading to the ground state of the final nucleus or to the double isobaric analog state.