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

TL;DR

This paper reports the first observation of a singly Cabibbo-suppressed decay of the $\Lambda_c^+$ baryon into $\Sigma^- ext{ extonehalf}K^+ ext{ extonehalf} ext{ extonehalf}$, measuring its branching fraction and comparing it to a favored decay to explore decay dynamics.

Contribution

It presents the first observation and measurement of the branching fraction of a specific Cabibbo-suppressed $\Lambda_c^+$ decay involving $\Sigma^-$, providing new insights into decay mechanisms.

Findings

First observation of the decay with 6.4σ significance.

Measured branching fraction: (3.8 ± 1.3 (stat) ± 0.2 (syst))×10⁻⁴.

The ratio of branching fractions deviates from simple Cabibbo-suppressed expectations.

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 $(3.8\pm1.3_{\rm stat}\pm0.2_{\rm syst})\times 10^{-4}$ 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.