Pion double-charge exchange onO16andO18

The zero-degree differential cross section for pion double-charge exchange on ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}({\pi }^{+},{\pi }^{+-}){}_{}{}^{18}{}_{}{}^{}\mathrm{Ne}$ was measured at three incident pion energies and found to be 2.00±0.34, 2.19±0.44, and 1.67±0.38 μb/sr at 139, 126, and 95 MeV, respectively. A similar measurement for ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ at an energy of 145 MeV resulted in a value of 0.87 ± 0.21 μb/sr. The ratio of the ground-state transitions near 140 MeV is $\frac{\sigma \left({}_{}{}^{18}{}_{}{}^{}\mathrm{O}\right)}{\sigma \left({}_{}{}^{16}{}_{}{}^{}\mathrm{O}\right)}=2.3\mathrm{}\pm 0.7$. The mass excess determined for ${}_{}{}^{16}{}_{}{}^{}\mathrm{Ne}$ is 24.4 ± 0.5 MeV. The experimental setup and data analysis are discussed in detail. Results are compared with various calculations and discussed from the standpoint of their implications for learning about reaction dynamics and nuclear structure. The reaction appears to be quite sensitive to ground-state correlations of the target.