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

We report the first observation of the decay $Lambda^{+}_{c} rightarrow p K^{+} pi^{-}$ 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 $mathcal{B}(Lambda^{+}_{c} rightarrow p K^{+} pi^{-})/mathcal{B}(Lambda^{+}_{c} rightarrow p K^{-} pi^{+})=(2.35pm0.27pm0.21)times10^{-3}$, where the uncertainties are statistical and systematic, respectively.