Measurement of the Branching Fraction of the Singly Cabibbo-Suppressed Decay $\Lambda_{c}^{+}\to\Lambda K^{+}$

TL;DR

This paper measures the branching fraction of the decay $\\Lambda_c^+ \to \Lambda K^+$ using BESIII data, providing a more precise value that challenges existing theoretical models and suggests underestimated non-factorizable effects.

Contribution

First precise measurement of the branching fraction for $\Lambda_c^+ \to \Lambda K^+$ decay, revealing discrepancies with theoretical predictions.

Findings

Measured branching fraction: $(6.21 \pm 0.44 \pm 0.26 \pm 0.34) \times 10^{-4}$.

Result is more precise than previous measurements.

Indicates non-factorizable contributions are underestimated in current models.

Abstract

We report a branching fraction measurement of the singly Cabibbo-suppressed decay $\Lambda_{c}^{+}\to\Lambda K^{+}$ using a data sample collected with the BESIII detector at the BEPCII storage ring. The data span center-of-mass energies from 4.599 to 4.950 GeV and correspond to an integrated luminosity of 6.44 fb$^{-1}$. The branching fraction of $\Lambda_{c}^{+}\to\Lambda K^{+}$ relative to that of the Cabibbo-favored decay $\Lambda_{c}^{+}\to\Lambda \pi^{+}$ is measured to be $\mathcal{R}=\frac{\mathcal{B}(\Lambda_{c}^{+}\to\Lambda K^{+})}{\mathcal{B}(\Lambda_{c}^{+}\to\Lambda \pi^{+})}=(4.78\pm0.34\pm0.20)\%$. Combining with the world-average value of $\mathcal{B}(\Lambda_{c}^{+}\to\Lambda \pi^{+})$, we obtain $\mathcal{B}(\Lambda_c^+\to\Lambda K^+)=(6.21\pm0.44\pm0.26\pm0.34)\times 10^{-4}$. Here the first uncertainties are statistical, the second systematic, and the third comes from the uncertainty of the $\Lambda_{c}^{+}\to\Lambda \pi^{+}$ branching fraction. This result, which is more precise than previous measurements, does not agree with theoretical predictions, and suggests that non-factorizable contributions have been under-estimated in current models.