Pion double charge exchange on Ca isotopes

A simple two-amplitude model introduced to relate pion double charge exchange on ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ is used to predict cross sections for ${}_{}{}^{42-48}{}_{}{}^{}\mathrm{Ca}$, based solely on experimental data for ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ and simple predictions for double isobaric analog transitions. The presence of the "forbidden" core component increases the expected ${}_{}{}^{42}{}_{}{}^{}\mathrm{Ca}$ cross sections by a factor of 6 above the double isobaric analog transition prediction and changes the expected ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$/${}_{}{}^{42}{}_{}{}^{}\mathrm{Ca}$ ratio by a factor of 4.5.