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First measurement of charmonium decay probabilities into a Σ0-hyperon pair and an η meson, refining the 12% rule.
Context
Hadronic decays of charmonia serve as a testing ground for quantum chromodynamics in the transition region between perturbative and non-perturbative regimes. The 12% rule predicts that the ratio of branching fractions for ψ(3686) and J/ψ decays into the same hadronic channel equals the ratio of their leptonic widths (~12%). However, violations are known—the famous "ρπ puzzle" and the isospin-violating decay ΛΛ̄π⁰. Related BESIII studies investigate rare decays of J/ψ and ψ(3686) into various baryon-antibaryon final states, gradually mapping out deviations from the 12% rule.
Methods
The analysis uses data from the BESIII detector at the BEPCII collider with record statistics: (10087 ± 44) × 10⁶ J/ψ events and (2712 ± 14) × 10⁶ ψ(3686) events. Σ0 and Σ̄0 are reconstructed via their decays to γΛ and γΛ̄, Λ → pπ⁻, and η → two photons. A kinematic fit with four constraints and a two-dimensional sideband method suppress background. Detection efficiency is determined by reweighting Monte Carlo events according to the observed Dalitz distribution, which is crucial due to the large difference from phase space.
Results
The decays J/ψ → Σ0Σ̄0η and ψ(3686) → Σ0Σ̄0η are observed for the first time. The measured branching fractions are B(J/ψ → Σ0Σ̄0η) = (7.5 ± 0.3± 0.8) × 10⁻⁵ and B(ψ(3686) → Σ0Σ̄0η) = (1.3 ± 0.1 ± 0.1) × 10⁻⁵. The ratio Q = (17.3 ± 1.5 ± 1.7)% agrees with the 12% rule within 3.0σ—a moderate deviation, but not as dramatic as in the ρπ channel. No significant intermediate resonances or threshold enhancements are found in the Σ0η and Σ0Σ̄0 invariant mass spectra.
Implications
This work adds a new data point to the systematics of 12% rule violations in baryonic final states. Unlike neighboring studies of rare J/ψ decays into hyperons and kaons, this is the first measurement of a channel with a Σ0 pair and an η meson, expanding the dataset for testing theoretical models. The absence of threshold enhancements in the Σ0Σ̄0 spectrum constrains hypotheses about baryonia and multiquark states, which are actively discussed for similar channels.
Future development
Accumulating more ψ(3686) statistics at BESIII and future experiments (STCF) will allow a more precise determination of Q and clarify whether the deviation from 12% is a statistical fluctuation or a real effect. The search for excited Σ* states in the Σ0η channel can be continued using partial wave analysis.
Impact
The results are important for charmonium physics and baryon spectroscopy, as well as for testing perturbative QCD predictions.
Next steps
Perform a similar analysis for other baryonic channels, e.g., J/ψ → Σ+Σ̄−η, and conduct a partial wave analysis to search for Σ* resonances.
Key open problems
This work is connected to the unresolved problem of the origin of 12% rule violations in hadronic charmonium decays and to the search for exotic baryonic states near threshold.
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
For the first time, the decays J/ψ → Σ0Σ̄0η and ψ(3686) → Σ0Σ̄0η are observed using BESIII data with record statistics. The branching fractions are measured to be (7.5 ± 0.3 ± 0.8) × 10⁻⁵ for J/ψ and (1.3 ± 0.1 ± 0.1) × 10⁻⁵ for ψ(3686). The ratio Q = (17.3 ± 1.5 ± 1.7)% agrees with the 12% rule within 3σ, and no intermediate states are found in the invariant mass spectra.
Where its strength is
This work adds a new data point to the systematics of violations of the 12% rule for baryonic final states, being the first to cover a channel with a Σ0 pair and an η meson. The absence of threshold enhancements in the Σ0Σ̄0 spectrum constrains hypotheses about baryonia and multiquark states.
Where it could go next
It might be interesting to compare the obtained ratio Q with similar measurements for other baryon-antibaryon channels with an η meson, for instance, J/ψ decays to ΛΛ̄η or ΞΞ̄η, to reveal the systematics of deviations from the 12% rule depending on the quark content of the final state.based on: Photon Detective: How the J/psi Particle DecaysarXiv:2603.23081
Closely related is the study of the rare decay of the Σ0 hyperon, where the branching fraction and magnetic moment have been measured. One could consider polarization observables in J/ψ → Σ0Σ̄0η to extract information on spin-dependent amplitudes and compare with model predictions.based on: Rare Decay of an Invisible ParticlearXiv:2608.16076v1
In the archive, there is a work on a rare decay observed for the first time, which may be useful for methodological comparisons when analyzing small branching fractions and suppressing background in similar channels.based on: Rare decay spotted for the first timearXiv:2604.26784
Worth trying
Check whether the ratio Q remains within errors for different regions of phase space, for example, as a function of the Σ0η invariant mass.
Use angular distributions to probe for intermediate resonances with higher sensitivity than in mass spectra.
Compare the measured branching fraction with theoretical estimates based on effective Lagrangians that include contributions from intermediate baryon resonances.
Why this may matter
This measurement extends the systematics of charmonium hadronic decays and may help understand the mechanism behind the violation of the 12% rule, which is important for testing QCD models in the non-perturbative regime.
Based on $$(10087 \pm 44) \times 10^6$$ $$J/\psi$$ and $$(2712 \pm 14) \times 10^6$$ $$\psi(3686)$$ events collected with the BESIII detector at the BEPCII collider, the hadronic decays $$J/\psi \to \Sigma^{0} \bar{\Sigma}^{0} \eta$$ and $$\psi(3686) \to \Sigma^{0} \bar{\Sigma}^{0} \eta$$ are observed for the first time. The corresponding branching fractions are measured to be $$\mathcal{B}(J/\psi \to \Sigma^{0} \bar{\Sigma}^{0}\eta)= (7.5 \pm 0.3 \pm 0.8) \times 10^{-5}$$ and $$\mathcal{B}(\psi(3686) \to \Sigma^{0} \bar{\Sigma}^{0}\eta)= (1.3\pm 0.1 \pm 0.1) \times 10^{-5}$$, respectively, where the first uncertainties are statistical, and the second systematic. The ratio $$\text{Q} \approx \frac{\mathcal{B}(\psi(3686) \to \Sigma^{0} \bar{\Sigma}^{0} \eta)}{\mathcal{B}(J/\psi \to \Sigma^{0} \bar{\Sigma}^{0} \eta)}$$ is determined to be $$(17.3 \pm 1.5 \pm 1.7)\%$$, which is con sistent with the 12\%-rule within 3.0$$\sigma$$.~No significant intermediate states or threshold enhancements are observed in the $$\Sigma^0$$($$\bar{\Sigma}^{0}$$)$$\eta$$ and $$\Sigma^0$$$$\bar{\Sigma}^{0}$$ invariant mass spectra.
