Charmed Baryons at Belle and Belle II

TL;DR

The paper investigates charmed-baryon decays in $e^+e^-$ collisions collected by Belle and Belle II, focusing on Λ_c and Ξ_c decay modes to illuminate the interplay of strong and weak forces, including non-spectator $W$-mediated processes. Using invariant-mass spectra and angular distributions, the study extracts branching fractions and the asymmetry parameter $\alpha_c$, providing both first observations (e.g., Cabibbo-suppressed decays) and improved measurements (e.g., $\Lambda_c^+ \to pK^0_S\pi^0$). Key results include precise branching-fraction ratios for multiple Ξ_c decays, the first measurements of Cabibbo-allowed $\Xi_c^0$ decays to $\Xi^0\pi^0$, $\Xi^0\eta$, and $\Xi^0\eta'$, and a notably large negative $\alpha_c$ value, all contributing to tests of flavor symmetry models. Collectively, these measurements constrain non-spectator weak dynamics in charm and favor $SU(3)_f$ flavor-symmetry predictions, enhancing our understanding of weak transitions within the charmed-baryon sector.

Abstract

We present the recent results on charm baryon production and decays at Belle and Belle II experiments using a 1.4 ab$^{-1}$ data sample of $e^+ e^-$ collision collected at center-of-mass energies near the $Υ(nS)$ resonances. The collected data contain a large number of $e^+ e^- \to c \bar{c}$ events that produce charmed baryons. We report on several studies of the $Λ_c$ and $Ξ_c$ decays to determine their branching fractions.

Figures (4)

• Figure 1: Invariant mass spectra of $\Xi_c^+$ candidates from $\Xi_c^+ \to \Sigma^+K_S^0$ (a, d) $\Xi_c^+ \to \Xi^0 \pi^+$ (b, e) and $\Xi_c^+ \to \Xi^+K_S^+$ (c, f) decays reconstructed in (top) Belle and (bottom) Belle II data.
• Figure 2: The invariant mass spectra of $\Lambda_c^+$ candidates for $\Lambda_c^+ \to pK^-\pi^+$ (a) and $\Lambda_c^+ \to pK^0_S\pi^0$ (b). The total fit is represented by a solid red curve, the signal by a dashed blue curve, and the background by a long-dashed green curve.
• Figure 3: The invariant mass spectra of $\Xi_c^0$ candidates from (a, d) $\Xi_c^0 \to \Xi^0\pi^0$, (b, e) $\Xi_c^0 \to \Xi^0\eta$, and (c, f) $\Xi_c^0 \to \Xi^0\eta'$ decays reconstructed in Belle (top) and Belle II (bottom) data.
• Figure 4: Efficiency-corrected $\Xi_c^0$ signal yields in bins of $cos\theta_{\Xi^0}$ from the (a) Belle and (b) Belle II datasets. The lines show linear regression results.