First observation of $Λ_{c}(2595)^{+} \to Λ^{+}_{c}π^0π^0$ and $Λ_{c}(2625)^{+}\to Λ^{+}_{c}π^0π^0$

TL;DR

This work reports the first observations of Λ_c(2595)^+ → Λ_c^+ π^0π^0 and Λ_c(2625)^+ → Λ_c^+ π^0π^0 using e^+e^− data at √s ≈ 4.9 GeV with the BESIII detector, achieving significances of $5.3\sigma$ and $8.3\sigma$ respectively. A model‑independent tag‑and‑recoil method is employed with three hadronic tag modes and a partial reconstruction strategy to measure absolute branching fractions; the results are $\mathcal{B}(Λ_c(2595)^+ → Λ_c^+ π^0π^0) = (59.5 ± 11.1_{stat.} ± 7.9_{syst.})\%$ and $\mathcal{B}(Λ_c(2625)^+ → Λ_c^+ π^0π^0) = (41.0 ± 5.2_{stat.} ± 3.3_{syst.})\%$. The ratio to the corresponding $π^+π^−$ decays for Λ_c(2625)^+ is $0.8 ± 0.2$, and the 2595^+ mode is broadly consistent with the threshold effect expectation within uncertainties, providing crucial inputs for determining the couplings $h_2$ and $h_8$ in heavy hadron chiral perturbation theory. Overall, the results offer a first experimentally robust, model‑independent view of these π^0π^0 transitions and test isospin symmetry in these decays.

Abstract

By analysing $e^+e^-$ annihilation data corresponding to an integrated luminosity of 368.48~pb$^{-1}$ collected at the centre-of-mass energies of $\sqrt{s} = 4.918$ and $4.951$~GeV with the BESIII detector, we report the first observation of $Λ_{c}(2595)^{+}$ and $Λ_{c}(2625)^{+}\to Λ^{+}_{c}π^0π^0$ with statistical significances of 7.9$σ$ and 11.8$σ$, respectively. The branching fractions of $Λ_{c}(2595)^{+}$ and $Λ_{c}(2625)^{+}\to Λ^{+}_{c}π^0π^0$ are measured to be $(59.5 \pm 11.1_{\rm stat.} \pm 7.9_{\rm syst.}) \%$ and $(41.0 \pm 5.2_{\rm stat.} \pm 3.3_{\rm syst.}) \%$, respectively. The absolute branching fraction of $Λ_{c}(2595)^{+}$ is consistent with the expectation of the mechanism referred to as the threshold effect, proposed for the strong decays of $Λ_{c}(2595)^{+}$ within uncertainty.

Figures (2)

• Figure 1: The fits to the distributions $M_{\mathrm{recoil}}^{\mathrm{tag}}(\bar{\Lambda}^{-}_{c})$ at $\sqrt s = 4.918$ GeV (a) and 4.951 GeV (b). The black points with error bars are data. The solid curves represent the fit results, and the dashed curves describe individual components including both signals and backgrounds. The contribution of $e^+e^- \to \Sigma_{c}\bar{\Sigma}_{c}$ is negligible according to the fit results and cannot be seen evidently in the figures.
• Figure 2: The fits to the distributions $M^{\rm sig}_{\rm recoil}(\bar{\Lambda}^{-}_{c})$ at $\sqrt s = 4.918$ GeV (a) and 4.951 GeV (b). The black points with error bars are data. The solid curves represent the fit results, and the dashed curves describe individual components including both signals and backgrounds.