Using $567{\mathrm{pb}}^{-1}$ of data collected with the BESIII detector at a center-of-mass energy of $\sqrt{s}=4.599\mathrm{GeV}$, near the ${\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c^{-}$ threshold, we study the singly Cabibbo-suppressed decays ${\mathrm{\Lambda }}_c^{+}\to p{\pi }^{+}{\pi }^{-}$ and ${\mathrm{\Lambda }}_c^{+}\to p{K}^{+}{K}^{-}$. By normalizing with respect to the Cabibbo-favored decay ${\mathrm{\Lambda }}_c^{+}\to p{K}^{-}{\pi }^{+}$, we obtain ratios of branching fractions: $[\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to p{\pi }^{+}{\pi }^{-})/\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to p{K}^{-}{\pi }^{+})]=(6.70\pm 0.48\pm 0.25)\%$, $[\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to p\varphi )/\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to p{K}^{-}{\pi }^{+})]=(1.81\pm 0.33\pm 0.13)\%$, and $[\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to p{K}^{+}{K}_{\mathrm{non}-\varphi }^{-})/\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to p{K}^{-}{\pi }^{+})]=(9.36\pm 2.22\pm 0.71)\times {10}^{-3}$, where the uncertainties are statistical and systematic, respectively. The absolute branching fractions are also presented. Among these measurements, the decay ${\mathrm{\Lambda }}_c^{+}\to p{\pi }^{+}{\pi }^{-}$ is observed for the first time, and the precision of the branching fraction for ${\mathrm{\Lambda }}_c^{+}\to p{K}^{+}{K}_{\mathrm{non}\text{−}\varphi }^{-}$ and ${\mathrm{\Lambda }}_c^{+}\to p\varphi$ is significantly improved.

• Received 28 July 2016
• Corrected 29 December 2017

DOI:https://doi.org/10.1103/PhysRevLett.117.232002