Phys. Rev. D 109, 032003 (2024) - First observation of ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}{K}^{+}{\ensuremath{\pi}}^{0}$ and evidence of ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}{K}^{+}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$

Open Access

First observation of $Λ_{c}^{+} \to Λ K^{+} π^{0}$ and evidence of $Λ_{c}^{+} \to Λ K^{+} π^{+} π^{-}$

M. Ablikim et al. (BESIII Collaboration)

Phys. Rev. D 109, 032003 – Published 7 February 2024

Abstract

We present the first observation of the singly Cabibbo-suppressed decay $Λ_{c}^{+} \to Λ K^{+} π^{0}$ with a significance of $5.7 σ$ and the first evidence of $Λ_{c}^{+} \to Λ K^{+} π^{+} π^{-}$ decay with a significance of $3.1 σ$ , based on $e^{+} e^{-}$ annihilation data recorded by the BESIII detector at the BEPCII collider. The data correspond to an integrated luminosity of $6.4 {fb}^{- 1}$ , in the center-of-mass energy range from 4.600 to 4.950 GeV. We determine the branching fractions of $Λ_{c}^{+} \to Λ K^{+} π^{0}$ and $Λ_{c}^{+} \to Λ K^{+} π^{+} π^{-}$ relative to their Cabibbo-favored counterparts to be $\frac{B (Λ_{c}^{+} \to Λ K^{+} π^{0})}{B (Λ_{c}^{+} \to Λ π^{+} π^{0})} = (2.09 \pm 0.3 9_{stat} \pm 0.0 7_{syst}) \times 10^{- 2}$ and $\frac{B (Λ_{c}^{+} \to Λ K^{+} π^{+} π^{-})}{B (Λ_{c}^{+} \to Λ π^{+} π^{+} π^{-})} = (1.13 \pm 0.4 1_{stat} \pm 0.0 6_{syst}) \times 10^{- 2}$ , respectively. Moreover, by combining our measured result with the world average of $B (Λ_{c}^{+} \to Λ π^{+} π^{0})$ , we obtain the branching fraction $B (Λ_{c}^{+} \to Λ K^{+} π^{0}) = (1.49 \pm 0.2 7_{stat} \pm 0.0 5_{syst} \pm 0.0 8_{ref}) \times 10^{- 3}$ . This result significantly departs from theoretical predictions based on quark $S U (3)$ flavor symmetry, which is underpinned by the presumption of meson pair $S$ -wave amplitude dominance.

Received 21 November 2023
Accepted 9 January 2024

DOI:https://doi.org/10.1103/PhysRevD.109.032003

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Published by the American Physical Society