Study of the 1450-Mev $p{\pi }^{+}{\pi }^{-}$ Enhancement in the Reaction $K^{+}p\to K^{+}{\pi }^{+}{\pi }^{-}p$ at 5.5 BeV/c

A highly peripheral $p{\pi }^{+}{\pi }^{-}$ enhancement centered near 1450 MeV, observed in $K^{+}p\to K^{+}{\pi }^{+}{\pi }^{-}p$ at 5.5 BeV/c, is shown to be consistent with a ${\Delta }^{++}{\pi }^{-}$ system with $I=\frac{1}{2}$. We observe a large asymmetry in the ${\Delta }^{++}{\pi }^{-}$ angular distribution which is not consistent with a pure resonant effect. Dissociation-type models fit the data reasonably well when cuts are made on the $K^{+}{\pi }^{-}$ mass, and this is interpreted as evidence for diffractive $K^{+}{\pi }^{-}$ virtual scattering in this $K^{+}{\pi }^{-}$ mass region.