The pion spectra observed in the inclusive double-charge-exchange reactions ${}_{}{}^4{}_{}{}^{}\mathrm{He}$(${\pi }^{+}$,${\pi }^{\mathrm{-}}$)4p and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$(${\pi }^{\mathrm{-}}$,${\pi }^{+}$)4n are strikingly different from those in heavier nuclei, exhibiting a prominent peak at high outgoing pion energies. The shapes of these spectra, while qualitatively consistent with two sequential single-charge-exchange processes, are not yet quantitatively understood.

• Received 4 August 1986

DOI:https://doi.org/10.1103/PhysRevLett.57.3152