Measurements of Branching fractions of $\Lambda_c^+\to\Lambda K^+ \pi^0$ and $\Lambda_c^+\to\Lambda K^+ \eta$ at Belle and Belle II
| Abstract | We present a study of the three-body, singly Cabibbo-suppressed decays $\Lambda_c^+ \to \Lambda K^+ \pi^0$ and $\Lambda_c^+ \to \Lambda K^+ \eta$ using data recorded with the Belle and Belle~II detectors at the KEKB and SuperKEKB $e^+ e^-$ colliders. The data samples correspond to integrated luminosities of 980\invfb and 570\invfb, respectively. We measure their branching-fraction ratios relative to the Cabibbo-favored decay $\Lambda_c^+ \to \Lambda \pi^+ \pi^0$ as $\mathcal{B}(\Lambda_c^+ \to \Lambda K^+ \pi^0)/\mathcal{B}(\Lambda_c^+ \to \Lambda \pi^+ \pi^0)=(1.82 \pm 0.07 \pm 0.07)\%$, with significantly improved precision compared to the previous measurement, and $\mathcal{B}(\Lambda_c^+ \to \Lambda K^+ \eta)/\mathcal{B}(\Lambda_c^+ \to \Lambda \pi^+ \pi^0)=(8.73 \pm 0.35 \pm 0.43)\times10^{-3}$, corresponding to the first observation of the $\Lambda_c^+ \to \Lambda K^+ \eta$ decay with a statistical significance exceeding 10 standard deviations. The first and second uncertainties are statistical and systematic, respectively. Using the world-average value of the branching fraction for $\Lambda_c^+ \to \Lambda \pi^+ \pi^0$, we obtain the branching fractions $\mathcal{B}(\Lambda_c^+ \to \Lambda K^+ \pi^0)=(1.29\pm 0.05\pm 0.05\pm 0.06)\times10^{-3}$ and $\mathcal{B}(\Lambda_c^+ \to \Lambda K^+ \eta)=(6.20\pm 0.25\pm 0.31\pm 0.30)\times10^{-4}$, where the third uncertainty arises from the uncertainty in the world-average value of $\mathcal{B}(\Lambda_c^+ \to \Lambda \pi^+ \pi^0)$. The measured $\mathcal{B}(\Lambda_c^+\to\Lambda K^+\eta)$ is significantly larger than predictions based on $SU(3)$ flavor symmetry. |
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| Tags | Belle Run 1 Run 2 (partial) |
| Working group | Charm |
| Principal authors | @ Junxi Cui, Chengping Shen |
| Reference | submitted to PRD |
| Links | arXiv:2610.31377 |