Interference effects in pion double charge exchange

Pion double charge exchange (${\pi }^{+}$,${\pi }^{-}$) has been measured using targets of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ from 80 to 292 MeV at a laboratory angle of 5°. The magnitude and energy dependence of the cross section for the double-analog transition is qualitatively described in terms of a direct double-analog amplitude and a two-step nonanalog amplitude.