First Observation of Doubly Cabibbo-Suppressed Decay of a Charmed Baryon: ${\mathrm{\Lambda }}_c^{+}\to p{K}^{+}{\pi }^{-}$

We report the first observation of the decay $\Lambda^{+}{c} \rightarrow p K^{+} \pi^{-}$usinga980$$\mathrm{f}{\mathrm{b}}^{-1}$$ data sample collected by the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. This is the first doubly Cabibbo-suppressed decay of a charmed baryon to be observed. We measure the branching ratio of this decay with respect to its Cabibbo-favored counterpart to be $$\mathcal{B}$(\Lambda^{+}{c} \rightarrow p K^{+} \pi^{-})/$\mathcal{B}$(\Lambda^{+}_{c} \rightarrow p K^{-} \pi^{+})=(2.35\pm0.27\pm0.21)\times10^{-3}$, where the uncertainties are statistical and systematic, respectively.