A sample of 198 events, corresponding to a cross section of 110 ± 15 μb, has been isolated of the baryon-diffractive-dissociation process $n\to p{\pi }^{-}{\pi }^0$ for three-body masses less than 2.5 ${\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c}}^2$. These dissociations are induced by 12-GeV/c $K^{-}$ mesons. To isolate this process from background, it is necessary to observe the final-state proton explicitly by its ionization in the bubble chamber. The three-body mass spectrum seems different from that of the $n{\pi }^{+}{\pi }^{-}$ neutron diffractive breakup. A ${\Delta }^0$ signal is seen as well as possible $N_{1470}^{*}$, but no clear ${\Delta }^{+}$ is observed. The angular distribution of the proton in the $p{\pi }^{+}{\pi }^{-}$ rest frame indicates that a multiperipheral mechanism is present.

• Received 30 May 1978

DOI:https://doi.org/10.1103/PhysRevD.19.43