Mass dependence of pion double charge exchange

Data are presented for pion double charge exchange on targets of ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$, ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$, ${}_{}{}^{80}{}_{}{}^{}\mathrm{Se}$, ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$, and ${}_{}{}^{118}{}_{}{}^{}\mathrm{Sn}$. These and earlier data are used to examine the mass dependence of double-isobaric-analog transitions and nonanalog ground-state-to-ground-state transitions in the energy region $T_{\pi }$=100 to 300 MeV. The implications of the mass dependence to the interpretations of the underlying reaction mechanisms of double charge exchange are discussed.