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First Observation of Doubly Cabibbo-Suppressed Decay of a Charmed Baryon: $Λ^{+}_{c} \rightarrow p K^{+} π^{-}$

We report the first observation of the decay $Λ^{+}_{c} \rightarrow p K^{+} π^{-}$ using a 980 $\mathrm{fb^{-1}}$ 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 $\mathcal{B}(Λ^{+}_{c} \rightarrow p K^{+} π^{-})/\mathcal{B}(Λ^{+}_{c} \rightarrow p K^{-} π^{+})=(2.35\pm0.27\pm0.21)\times10^{-3}$, where the uncertainties are statistical and systematic, respectively.