Observation of the Singly Cabibbo-Suppressed Decay ${\Lambda }_c^{+}\to {\Sigma }^{-}{K}^{+}{\pi }^{+}$

Abstract

The singly Cabibbo-suppressed decay ${\Lambda }_c^{+}\to {\Sigma }^{-}{K}^{+}{\pi }^{+}$ is observed for the first time with a statistical significance of $6.4\sigma$ by using 4.5 fb${}^{-1}$ of $e^{+}{e}^{-}$ collision data collected at center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at BEPCII. The absolute branching fraction of ${\Lambda }_c^{+}\to {\Sigma }^{-}{K}^{+}{\pi }^{+}$ is measured to be $(3.8\pm 1.3_{\mathrm{stat}}\pm 0.2_{\mathrm{syst}})\times 10^{-4}$ in a model-independent approach. This is the first observation of a Cabibbo-suppressed ${\Lambda }_c^{+}$ decay involving ${\Sigma }^{-}$ in the final state. The ratio of branching fractions between ${\Lambda }_c^{+}\to {\Sigma }^{-}{K}^{+}{\pi }^{+}$ and the Cabibbo-favored decay ${\Lambda }_c^{+}\to {\Sigma }^{-}{\pi }^{+}{\pi }^{+}$ is calculated to be $(0.4\pm 0.1)s_c^2$, where $s_c\equiv \sin {\theta }_c=0.2248$ with ${\theta }_c$ the Cabibbo mixing angle. This ratio significantly deviates from $1.0s_c^2$ and provides important information for the understanding of nonfactorization contributions in ${\Lambda }_c^{+}$ decays.

arXiv comment8 pages, 2 figures

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