The (${\mathrm{\pi }}^{+}$,${\mathrm{\pi }}^{\mathrm{-}}$) double-charge-exchange reaction for pion energies of 200 to 1400 MeV is calculated with a zero-parameter Glauber theory that includes spin flip and pion absorption. Differential cross sections and excitation functions are obtained for ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ targets. Results for ${\mathit{T}}_{\mathrm{\pi }}$=300–525 MeV are compared with recent experimental results and suggest a new quenching process. We have calculated effects of medium polarization on the isovector pion operator and find a strong reduction in good agreement with data. A pronounced dip in the cross section near ${\mathit{T}}_{\mathrm{\pi }}$=1300 MeV offers a unique testing ground for unconventional mechanisms.

• Received 22 May 1992

DOI:https://doi.org/10.1103/PhysRevLett.70.146