Observation of the Singly Cabibbo-Suppressed Decay $\hat{I}{›}_c^{+}\to \hat{I}{\pounds }^{-}{K}^{+}\ddot{I}{€}^{+}$

Abstract

The singly Cabibbo-suppressed decay $\hat{I}{›}_c^{+}\to \hat{I}{\pounds }^{-}{K}^{+}\ddot{I}{€}^{+}$ is observed for the first time with a statistical significance of $6.4\ddot{I}ƒ$ 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 $\hat{I}{›}_c^{+}\to \hat{I}{\pounds }^{-}{K}^{+}\ddot{I}{€}^{+}$ 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 $\hat{I}{›}_c^{+}$ decay involving $\hat{I}{\pounds }^{-}$ in the final state. The ratio of branching fractions between $\hat{I}{›}_c^{+}\to \hat{I}{\pounds }^{-}{K}^{+}\ddot{I}{€}^{+}$ and the Cabibbo-favored decay $\hat{I}{›}_c^{+}\to \hat{I}{\pounds }^{-}\ddot{I}{€}^{+}\ddot{I}{€}^{+}$ is calculated to be $(0.4\pm 0.1)s_c^2$, where $s_c\equiv \sin \hat{I}{¸}_c=0.2248$ with $\hat{I}{¸}_c$ the Cabibbo mixing angle. This ratio significantly deviates from $1.0s_c^2$ and provides important information for the understanding of nonfactorization contributions in $\hat{I}{›}_c^{+}$ decays.

8 pages, 2 figures