Observation of Cabibbo-suppressed and W-exchange Λ_c ⁺ baryon decays

We present measurements of the Cabibbo-suppressed decays Λ ⁺ _c → Λ⁰K ⁺ and Λ ⁺ _c → Λ⁰K ⁺ (both first observations), Λ ⁺ _c → Λ ⁺ K ⁺ π ^- (seen with large statistics for the first time), Λ ⁺ _c → _pK ⁺ K ^- and Λ ⁺ _c → pφ (measured with improved accuracy). Improved branching ratio measurements for the decays Λ ⁺ _c → Λ ⁺ K ⁺ K ^- and Λ ⁺ _c → Λ ⁺ φ, which are attributed to W-exchange diagrams, are shown. We also present the first evidence for {equation presented} and set an upper limit on the non-resonant decay Λ ⁺ _c → Λ ⁺ K ⁺ K^-. This analysis was performed using 32.6 fb^-1 of data collected by the Belle detector at the asymmetric e ⁺ e ^- collider KEKB.