Amplitude analysis and branching fraction measurement of $J/ψ\to Λ\barΣ^0η+\mathrm{c.c}$

TL;DR

This work reports the first partial-wave analysis of the charmonium decay $J/ψ\to Λ\bar{Σ}^0η$ using a BESIII data set of $(10087\pm44)\times10^6$ $J/ψ$ events. The analysis identifies two Λ* contributions with $J^P=1/2^-$ and $1/2^+$, consistent with the Λ(1670) and a Λ(1810)-like state, and provides their masses, widths, and product branching fractions, with high statistical significance. The branching fraction $\mathcal{B}(J/ψ\to Λ\bar{Σ}^0η)$ is measured to be $(3.44\pm0.11\pm0.13)\times10^{-5}$, and systematic studies are performed for both the event selection and the PWA, reinforcing the robustness of the results. These measurements contribute to a more precise map of Λ* spectroscopy and demonstrate the efficacy of a helicity-amplitude, isobar-model PWA in charmonium decays. Overall, the study enhances understanding of nonperturbative QCD in hyperon production and helps clarify the structure of Λ resonances near ηΛ thresholds.

Abstract

Based on a sample of $(10087\pm44)\times10^{6}$ $J/ψ$ events collected with the BESIII detector, a partial-wave analysis of $ J/ψ\to Λ\bar{ Σ}^0η+\mathrm{c.c} $ is performed for the first time. The dominant contributions are found to be excited $Λ$ states with $J^P=1/2^-$ and $J^P=1/2^+$ in the $ηΛ$ mass spectra. The measured masses and widths are $M=1668.8\pm3.1\pm21.2$ MeV/$c^2$ and $Γ=52.7\pm4.2\pm17.8$ MeV for the $Λ(1670)$, and $M=1881.5\pm16.5\pm20.3$ MeV/$c^2$ and $Γ=82.4\pm18.2\pm8.9$ MeV for the $Λ(1810)$, respectively. The branching fraction is determined to be $ \mathcal{B}(J/ψ\to Λ\bar{ Σ}^0η+\mathrm{c.c}) $ = $(3.44 \pm 0.11 \pm 0.13) \times 10^{-5}$. The first uncertainties are statistical and the second systematic.

Figures (6)

• Figure 1: The distributions of (a) $M ( p \pi^-$) and (b) $M ( \bar{p} \pi ^+)$. Dots with error bars represent data, the blue line is the simulated signal shape, and the yellow line denotes the background from the inclusive MC sample. The red arrows denote the $\Lambda$ and $\bar{\Lambda}$ mass windows.
• Figure 2: The distributions of (a) $M (\gamma\Lambda$) and (b) $M (\gamma\bar{\Lambda})$. Dots with error bars represent data, the blue line is the simulated signal shape, and the yellow line denotes the background from the inclusive MC sample. The $\Sigma^0$ and $\bar{\Sigma}^0$ signal region is shown with the red arrows and $\Sigma^0$ and $\bar{\Sigma}^0$ sideband ranges are shown with the short green arrows.
• Figure 3: The Dalitz plots of (a) $J/\psi \to\bar{\Lambda}\Sigma^0\eta$ and (b) $J/\psi \to\Lambda\bar{\Sigma}^0\eta$ events in the $\Sigma$ signal region from data.
• Figure 4: The distributions of (a) $M ( \eta \Lambda )$, (b) $M ( \Lambda \bar{\Sigma}^0)$ and (c)$M ( \eta \bar{\Sigma}^0 )$. The black lines are the total PWA results, the gray histograms represent the background, while the red lines are $\Lambda(1/2^-)$ and the orange lines are $\Lambda(1/2^+)$.
• Figure 5: The distributions of (a) $\cos{\theta_{\eta/\eta\Lambda}}$, (b) $\cos{\theta_{\Lambda/\Lambda\bar{\Sigma}}}$ and (c)$\cos{\theta_{\bar{\Sigma}/\eta\bar{\Sigma}}}$. The black lines are the total PWA results. The gray histograms represent the background. The red and orange lines show the components of $\Lambda(1/2^-)$ and $\Lambda(1/2^+)$, respectively.