Target mass dependence of isotensor double charge exchange: Evidence for deltas in nuclei

Measurements of forward-angle cross sections for double charge exchange on ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ at 164 MeV incident pion energy suggest an $A^{-\frac{4}{3}}$ dependence for the cross section. This $A$ dependence is shown to provide evidence for $\Delta$ components in the nuclear wave function.