The doubly Cabibbo-suppressed decay $D^{+}\to K^{+}{\pi }^{-}{\pi }^{+}$

The Fermilab E791 Collaboration

We report the observation of the doubly Cabibbo-suppressed decay $D^{+}\to K^{+}{\pi }^{-}{\pi }^{+}$ in data from Fermilab charm hadroproduction experiment E791. With a signal of 59 \pm 13 events…