arXiv subjects

H. -R. Bao

Publications and source records attributed to H. -R. Bao.

At least 73 records · Page 4Linked to original sources

arXiv2026

Measurement of the branching fraction of $η\to μ^+ μ^-$ and search for $η\to e^+ e^-$

We analyze the decay of $η\rightarrow \ell^+\ell^-(\ell=e, μ)$ via $J/ψ\rightarrowγη'$ and $η'\rightarrowπ^+π^-η$, based on (10087 $\pm$ 44) $\times$ 10$^{6}$ $J/ψ$ events collected with the BESIII detector at the BEPCII storage rings. The branching fraction of $η\rightarrowμ^+ μ^-$ is measured to be $(5.8 \pm 1.0_{\rm stat} \pm 0.2_{\rm syst}) \times 10^{-6}$, which is consistent with the previous measurements and theoretical expectations. In addition, no significant $η\to e^+e^-$ signal is observed in the $e^+ e^-$ invariant mass spectrum, and an improved upper limit of ${\cal B}(η\to e^+ e^-) < 2.2 \times 10^{-7}$ is set at 90\% confidence level.

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arXiv2026

Multi-channel joint analysis of the exotic charmonium-like state $T_{c\bar{c}}(4020)$

This paper reports the first multi-channel joint analysis to identify the properties of the exotic charmonium-like state $T_{c\bar{c}}(4020)$ via the electron-positron annihilation process $e^{+}e^{-}\toπ^{+}T_{c\bar{c}}(4020)^{-}+c.c$. A partial wave analysis is performed simultaneously in three decay channels $T_{c\bar{c}}(4020)^{-}\to {D}^{*0}D^{*-}$, $π^{-}J/ψ$, and $π^{-}h_{c}$, based on data samples taken at $\sqrt{s}=4.395$ and $4.416\,\mathrm{GeV}$ with an integrated luminosity of $1598.9\,\mathrm{pb}^{-1}$ collected with the BESIII detector operating on the BEPCII collider. For the first time, the spin-parity of the $T_{c\bar{c}}(4020)^{-}$ is determined to be $J^{P}=1^{+}$ with a significance $11.7σ$. Pole positions are extracted on the Riemann sheets with three branch points in the complex energy plane. Furthermore, the relative branching fractions are obtained as $\mathcal{B}[T_{c\bar{c}}(4020)^{-}\toπ^{-}J/ψ]/\mathcal{B}[T_{c\bar{c}}(4020)^{-}\to{D}^{*0}D^{*-}]=(3.6\pm0.6\pm1.6)\times10^{-3}$ and $\mathcal{B}[T_{c\bar{c}}(4020)^{-}\toπ^{-}h_{c}]/\mathcal{B}[T_{c\bar{c}}(4020)^{-}\to{D}^{*0}D^{*-}]=(8.9\pm1.3\pm2.3)\times10^{-2}$, where the first uncertainties are statistical, and the second are systematic.

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arXiv2026

Precise measurement of the form factors in $D^0\rightarrow K^(892)^-\ell^+ν_{\ell}$ and observation of $D^0\rightarrow K_2^(1430)^-\ell^+ν_{\ell}$

We report a study of the semileptonic decays $D^0 \rightarrow \bar{K}^0π^-\ell^+ν_{\ell}$ (where $\ell=e,~μ$) based on a sample of $20.3~\mathrm{fb}^{-1}$ of $e^+e^-$ annihilation data collected at a center-of-mass energy of 3.773~GeV with the BESIII detector at the BEPCII collider. Based on an investigation of the decay dynamics in $D^0 \rightarrow \bar{K}^0π^-\ell^+ν_{\ell}$ decays, a $\mathcal{D}-$wave component of $D^0\rightarrow K_2^*(1430)^-\ell^+ν_{\ell}$ is observed for the first time with a statistical significance of $8.0σ$, in addition to the dominant $K^*(892)^-$ and $\mathcal{S}-$wave components. The $\mathcal{D}-$wave component is determined to account for $(0.092 \pm 0.028_{\rm stat} \pm 0.018_{\rm syst})\%$ of the total decay rate. The branching fractions of the dominant $K^*(892)^-$ components are measured as $\mathcal{B}(D^0\rightarrow K^{*}(892)^-e^+ν_{e}) = (2.043 \pm 0.018_{\rm stat} \pm 0.012_{\rm syst})\%$ and $\mathcal{B}(D^0\rightarrow K^{*}(892)^-μ^+ν_μ) = (1.964 \pm 0.018_{\rm stat} \pm 0.012_{\rm syst})\%$, which are the most precise measurements to date and represent significant improvements over the previous world averages. The hadronic form-factor parameters are measured to be $r_{V} = V(0)/A_1(0) = 1.444 \pm 0.026_{\rm stat} \pm 0.010_{\rm syst}$, $r_{2} = A_2(0)/A_1(0) = 0.752 \pm 0.020_{\rm stat} \pm 0.004_{\rm syst}$, and $A_1(0)=0.618\pm0.002_{\rm stat} \pm0.004_{\rm syst}$, where $V(0)$ is the vector form factor and $A_{1,2}(0)$ are the axial-vector form factors evaluated at $q^2=0$. This is the most precise determination of the form-factor parameters to date measured in a $D\rightarrow K^*(892)$ transition. In addition, we report the first model-independent measurement of the $\mathcal{S}-$wave phase shift in the hadronic $\bar{K}^0π^-$ system.

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arXiv2026

Measurement of Born Cross Sections for $e^+e^-\toΣ^-\barΣ^+$ at $\sqrt{s}=3.51-4.95$ GeV and Observation of $ψ(3770)\toΣ^-\barΣ^+$

Using $e^+e^-$ collision data corresponding to an integrated luminosity of 44 fb$^{-1}$ collected with the BESIII detector at the BEPCII collider, we report the first measurement of Born cross sections and effective form factors for $e^+e^-\toΣ^-\barΣ^+$ at centre-of-mass energies between 3.51 and 4.95 GeV. With a fit to the $\sqrt{s}$-dependent dressed cross sections, the decay $ψ(3770)\toΣ^-\barΣ^+$ is observed for the first time with a significance of 5.5$σ$, including systematic uncertainties. Upper limits at the 90\% confidence level on the product of the branching fraction and the electronic partial width are provided for other possible charmonium(-like) states. The ratios of Born cross sections for the $Σ$ isospin-triplet states are determined and can be used to test the vector-meson-dominance model.

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arXiv2026

Precision Studies and Searches for CP Asymmetries in the Inclusive Decay $Λ_{c}^{+}\to ΛX$

Based on $e^+e^-$ annihilation data collected with the BESIII detector at center-of-mass energies from 4.600 to 4.699 GeV, corresponding to an integrated luminosity of 4.5 fb$^{-1}$, we present the first measurement of the longitudinal polarization of $Λ$ hyperons produced in the inclusive decay $Λ_c^+ \to ΛX$, where $X$ denotes any allowed final state. The polarizations are determined to be $\mathcal{P}_Λ = -0.393 \pm 0.055_{\mathrm{sta.}} \pm 0.020_{\mathrm{sys.}}$ and $\mathcal{P}_{\barΛ} = 0.288 \pm 0.056_{\mathrm{sta.}} \pm 0.017_{\mathrm{sys.}}$. We then search for CP violation using an asymmetry constructed from the $Λ$ polarization and the $Λ\to p π^-$ decay asymmetry parameters, and obtain $\mathcal{A}_{\mathrm{CP}}^{\mathrm{pol}} = 0.15 \pm 0.12_{\mathrm{sta.}} \pm 0.04_{\mathrm{sys.}}$. We also perform an updated measurement of the absolute branching fraction, resulted as $\mathcal{B}(Λ_c^+ \to ΛX) = (38.07 \pm 0.38_{\mathrm{sta.}} \pm 0.49_{\mathrm{sys.}})\%$, with precision improved by a factor of four relative to the current world average. A search for direct CP violation yields $\mathcal{A}_{\mathrm{CP}}^{\mathrm{dir}} = (1.5 \pm 1.0_{\mathrm{sta.}} \pm 1.0_{\mathrm{sys.}})\%$. No evidence for CP violation in inclusive charm baryon decays is observed.

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arXiv2026

Experimental study of the reaction $Ξ^{0}n\rightarrowΛΛX$ using $Ξ^{0}$-nucleus scattering

Using $(10087\pm44)\times10^{6}$$J/ψ$ events collected with the BESIII detector operating at the BEPCII storage ring in $2009$, $2012$, $2018$, and $2019$, we perform a search for the reaction $Ξ^0n\rightarrowΛΛX$, where $X$ denotes any additional final particles. Given the highly suppressed phase space for producing extra pions, the $X$ consists of either nothing or a photon, corresponding to the processes $Ξ^0 n \rightarrow ΛΛ$ and $Ξ^{0}n\rightarrowΛΣ^0\rightarrowΛΛγ$. The $Ξ^0$ comes from the decay of $J/ψ\rightarrowΞ^0\barΞ^0$, while the neutron originates from material of the beam pipe. A signal is observed for the first time with a statistical significance of 6.4$σ$. The cross section for the reaction $Ξ^0+{^9\rm{Be}}\rightarrowΛ+Λ+X$ is measured to be $(43.6\pm10.5_{\text{stat}}\pm11.1_{\text{syst}})$ mb at $P_{Ξ^0}\approx0.818$ GeV/$c$, where the first uncertainty is statistical and the second systematic. No significant $H$-dibaryon signal is observed in the $ΛΛ$ final state.

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arXiv2026

Improved measurements of the coherence factors and strong-phase differences in $D\to K^-π^+π^+π^-$ and $D\to K^-π^+π^0$ with quantum-correlated $D\bar{D}$ decays

Improved measurements of the coherence factors and strong-phase differences in $D\to K^-π^+π^+π^-$ and $D\to K^-π^+π^0$ decays are reported, using quantum-correlated $D\bar{D}$ pairs produced in $e^+e^-$ annihilation at a center-of-mass energy of $3.773\,\mathrm{GeV}$, where $D$ denotes a quantum superposition of the flavour-specific $D^{0}$ and $\bar{D}^{0}$ mesons. The analysis employs a dataset collected by the BESIII experiment, corresponding to an integrated luminosity of $7.93~\rm fb^{-1}$. The observables sensitive to the coherence factors and strong-phase differences are measured by reconstructing one $D$ meson in the signal mode and the other in a tag mode. These parameters provide essential inputs to the measurement of the angle $γ$ of the Cabibbo-Kobayashi-Maskawa Unitarity Triangle in the LHCb and Belle II experiments. The coherence factors are determined to be $R_{K3π}=0.51\pm0.04$ and $R_{Kππ^0}=0.75\pm0.03$, and the strong-phase differences are $δ_D^{K3π}=\left(182^{+14}_{-13}\right)^\circ$ and $δ_D^{Kππ^0}=\left(209^{+7}_{-8}\right)^\circ$, where the uncertainties include both statistical and systematic contributions. For $D\to K^-π^+π^+π^-$, the parameters have been further determined in four phase-space bins with improved precision compared to the previous BESIII results. The uncertainty on future $γ$ measurements from the knowledge of $D\to K^-π^+π^+π^-$ parameters is expected to be reduced to approximately 3.5$^\circ$.

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arXiv2026

Observation of $ψ(3686)\to γη(1405)$ via $η(1405)\to f_0(980)π^0$

The decay $ψ(3686)\toγπ^+π^-π^0$ is studied using a sample of $(2712.4\pm14.3)\times10^6$ $ψ(3686)$ events collected with the BESIII detector. The decay $η(1405)\toπ^+π^-π^0$ is observed for the first time in $ψ(3686)$ decays via the intermediate state $f_0(980)$ and the product branching fraction $\mathcal{B}(ψ(3686)\toγη(1405))\times\mathcal{B}(η(1405)\to f_0(980)π^0)\times \mathcal{B}(f_0(980)\toπ^+π^-)$ is determined to be $(3.77\pm0.43\pm0.29)\times10^{-7}$, where the first uncertainty is statistical and the second is systematic. The isospin-violating decay of $ψ(3686)\toγf_1(1285)\toγf_0(980)π^0\toγπ^+π^-π^0$ has been observed with signal significance of $2.9σ$. And the branching fraction $\mathcal{B}(ψ(3686)\toγf_1(1285)\toγf_0(980)π^0\toγπ^+π^-π^0)$ is determined to be $ (7.36\pm2.25\pm2.26)\times 10^{-8}$. Since no $η_c$ signal is evident in either the $π^+π^-π^0$ or $f_0(980)π^0$ mass spectrum, upper limits are set to be $\mathcal{B}(ψ(3686)\toγη_c)\times\mathcal{B}(η_c\toπ^+π^-π^0)<3.09\times10^{-7}$ and $\mathcal{B}(ψ(3686)\toγη_c)\times\mathcal{B}(η_c\to f_0(980)π^0)\times\mathcal{B}(f_0(980)\toπ^+π^-)<7.97\times10^{-8}$ at 90\% confidence level, respectively.

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arXiv2026

Search for the electromagnetic Dalitz decays $χ_{cJ}\to e^{+}e^{-}ϕ$

Using a data sample of $(2.712 \pm 0.014)\times10^{9}$ $ψ(3686)$ events collected at $\sqrt{s}=3.686$ GeV by the BESIII detector, we search for the rare electromagnetic Dalitz decays $χ_{cJ}\to e^+e^-ϕ~(J=0,\,1,\,2)$ via the radiative transitions $ψ(3686)\toγχ_{cJ}$. No statistically significant $χ_{cJ}\to e^+e^-ϕ$ signals are observed. The upper limits on the branching fractions of $χ_{cJ}\to e^+e^-ϕ~(J=0,\,1,\,2)$, excluding the $ϕ$ resonance to $e^+e^-$ final states, are set to be $2.4\times10^{-7},~6.7\times10^{-7}$ and $4.1\times10^{-7}$ at 90\% confidence level, respectively. This is the first search for the electromagnetic Dalitz transition of P-wave charmonium $χ_{cJ}$ states to a light vector meson.

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arXiv2026

Observation of a New Excited $Σ$ State in $ψ(3686)\to\bar{p}K^+Σ^0+c.c.$

Using a data sample of $(2712.4\pm14.3)\times10^6\ ψ(3686)$ events collected with the BESIII detector, a partial-wave analysis of $ψ(3686)\to\bar{p}K^+Σ^0+c.c.$ is performed. A new excited $Σ$ baryon state is observed with a statistical significance of $11.9σ$, and the mass and width are measured as $(2334.7\pm7.9\pm16.0)\;\mathrm{MeV}/c^2$ and $(206.3\pm9.5\pm18.4)\;\mathrm{MeV}$, respectively. The spin-parity of the new state is favored to be $3/2^-$, and the branching fraction of $ψ(3686)\to\barΣ(2330)^0Σ^0+c.c.$ is determined to be $(4.47\pm0.58\pm1.52)\times10^{-6}$. In addition, the branching fraction of $ψ(3686)\to\bar{p}K^+Σ^0+c.c.$ is determined to be either $(2.44\pm0.20\pm0.08)\times10^{-5}$ or $(1.73\pm0.29\pm0.06)\times10^{-5}$ by considering two solutions. The first uncertainties are statistical and the second systematic.

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arXiv2026

Measurement of the singly Cabibbo-suppressed decay $Λ_c^+\to pη'$ with Deep Learning

Using $4.5$ fb$^{-1}$ of $e^+e^-$ collision data collected with the BESIII detector at center-of-mass energies from 4.600 to 4.699 GeV, we report a measurement of the singly Cabibbo-suppressed decay $Λ_c^+ \to pη'$ with the single-tag method. To effectively distinguish the signal from the large backgrounds, we exploit a deep-learning classifier built on a Transformer-based neural network. Extensive validation and uncertainty quantification are carried out. The $Λ^+_c\to pη'$ signal is observed with a statistical significance of $3.4 σ$. The ratio of branching fractions of $\mathcal{B}{Λ^+_c\to pη'}/\mathcal{B}{Λ^+_c\to pω}$= $0.55\pm 0.22_{\rm{stat.}} \pm 0.05_{\rm{syst.}}$ is obtained, where the first uncertainty is statistical and the second systematic.

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arXiv2026

Search for a hypothetical gauge boson and dark photons in charmonium transitions

We report a direct search for a new gauge boson, $X$, with a mass of $17~\text{MeV}/c^2$, which could explain the anomalous excess of $e^+e^-$ pairs observed in the $^8\text{Be}$ nuclear transitions. The search is conducted in the charmonium decays $χ_{cJ}\to X J/ψ~(J=0,1,2)$ via the radiative transition $ψ(3686)\toγχ_{cJ}$ using $\left(2712.4\pm 14.3 \right)\times 10^6$ $ψ(3686)$ events collected with the BESIII detector at the BEPCII collider. No significant signal is observed, and the updated upper limit on the coupling strength of charm quark and the new gauge boson, $ε_c$, is set to be $|ε_c|<1.2\times 10^{-2}$ at $90\%$ confidence level. We also report new constraints on the mixing strength $ε$ between the Standard Model photon and dark photon $γ^\prime$ in the mass range from $5~\text{MeV}/c^2$ to $300~\text{MeV}/c^2$. The upper limits at $90\%$ confidence level vary within $(2.5-17.5)\times 10^{-3}$ depending on the $γ^\prime $ mass.

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arXiv2026

Study of $\barΛ$-$p$ Annihilation into Light Mesons

The annihilation of $\barΛ$-$p$ into light mesons is studied using $(10.087\pm0.044)\times10^{9}$ $J/ψ$ events collected with the BESIII detector at the BEPCII storage ring. The $\barΛ$ baryons are produced in the process $J/ψ\rightarrowΛ\barΛ$ and interact with the protons in the hydrogen nuclei in the cooling oil of the beam pipe. The reactions $\barΛp\rightarrow K^+π^+π^-$ and $K^+2π^+2π^-$ are observed for the first time, evidence for the reaction $\barΛp\rightarrow K^0_S2π^+π^-$ is found, and no significant signals are seen for the reactions $\barΛp\rightarrow K^0_Sπ^+$, $K^+3π^+3π^-$ and $2K^+K^-$. The cross sections of these reactions are also measured at $P_{\barΛ}\approx 1.074$ GeV/$c$. Furthermore, no significant structures are observed in the combinations of the final state particles for these reactions. The annihilation of $\barΛ$-$p$ into light mesons presents the similar behavior as $\bar{n}$-$p$ reactions in this energy region. These new measurements will serve as important inputs for the theoretical understanding of the antihyperon-nucleon interaction, and further contribute to understanding antibaryon-baryon interaction in a unified perspective.

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arXiv2026

Observation of $ψ(3686) \to Ξ^- K^0_S \barΩ^+ $+c.c

Using a sample of $(2.712\pm0.014) \times 10^{9}$ $ψ(3686)$ events collected with the BESIII detector at the electron positron collider BEPCII, the decay $ψ(3686) \to Ξ^- K^0_S \barΩ^+ +c.c.$ is observed for the first time, which has a significance of 5.9 standard deviations. The branching fraction of this decay is measured to be $(2.91\pm0.47\pm0.33)\times 10^{-6}$, where the first and second uncertainties are statistical and systematic, respectively. The ratio between $\mathcal{B}_{ψ(3686) \to Ξ^- K^0_S \barΩ^+ +c.c.}$ and $\mathcal{B}_{ψ(3686) \to Ω^- K^+ \barΞ^0 +c.c.}$ is determined to be $1.05\pm0.23\pm0.14 $, which deviates with the isospin symmetry conservation predicted value of 0.5 by $2.1σ$.

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arXiv2026

Study of $η\rightarrowπ^+π^-l^+l^-$

Using a sample of $(10087\pm44)\times10^{6}$ $J/ψ$ events accumulated with the BESIII detector, we analyze the decays $η\rightarrowπ^+π^-l^+l^-$ ($l=e$ or $μ$) via the process $J/ψ\rightarrowγη$. The branching fraction of $η\rightarrowπ^+π^-e^+e^-$ is measured to be $\mathcal{B}(η\rightarrowπ^+π^-e^+e^-)=(3.07\pm0.12_{\rm{stat.}}\pm0.19_{\rm{syst.}}) \times10^{-4}$. No signal events are observed for the $η\rightarrowπ^{+}π^{-}μ^{+}μ^{-}$ decay, leading to an upper limit on the branching fraction of $\mathcal{B}(η\rightarrowπ^{+}π^{-}μ^{+}μ^{-})<4.0\times10^{-7}$ at the 90\% confidence level. Furthermore, the $CP$-violation asymmetry parameter is found to be $\mathcal{A}_{CP}(η\rightarrowπ^{+}π^{-}e^{+}e^{-})=(-4.04\pm4.69_{\rm{stat.}}\pm0.14_{\rm{syst.}})\%$, showing no evidence of $CP$-violation with current statistics. Additionally, we extract the transition form factor from the decay amplitude of $η\rightarrowπ^+π^-e^+e^-$. Finally, axion-like particles are searched for via the decay $η\rightarrowπ^+π^-a, a\rightarrow e^+e^-$, and upper limits on this branching fraction relative to that of $η\rightarrowπ^+π^-e^+e^-$ are presented as a function of the axion-like particle mass in the range $5-200\ \mathrm{MeV}/c^{2}$.

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arXiv2026

First evidence for $D_s^+ \to f_1(1420) e^+ν_e$ and search for $D_s^+ \to f_1(1285) e^+ν_e$

Using $e^+e^-$ collision data corresponding to an integrated luminosity of 7.33~${\rm fb^{-1}}$ recorded by the BESIII detector at center-of-mass energies between 4.128 and 4.226~${\rm GeV}$, we present the first search for the semileptonic decays $D^+_s\to\ f_1(1420)e^+ν_e$ and $D^+_s\to\ f_1(1285)e^+ν_e$. The first evidence for the decay $D^+_s\to\ f_1(1420)e^+ν_e$ is found with a statistical significance of 3.4$σ$, and its product branching fraction $\mathcal{B}(D^+_s\to\ f_1(1420)e^+ν_e)\cdot\mathcal{B}(f_1(1420)\to\ K^+K^-π^0)$ is determined to be $\rm (4.5^{+2.0}_{-1.7}(stat) \pm0.4(syst)) \times 10^{-4} $, corresponding to an upper limit of $7.6 \times10^{-4}$ at the 90% confidence level. No significant signal of the decay $D^+_s\to\ f_1(1285)e^+ν_e$ is observed and the upper limit on the product branching fraction is set to be $\mathcal{B}(D^+_s\to\ f_1(1285)e^+ν_e)\cdot\mathcal{B}(f_1(1285)\to\ π^+π^-η) < 1.7\times10^{-4}$ at the 90% confidence level.

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arXiv2026

Helicity amplitude and branching fraction measurement of $χ_{cJ} \rightarrow Λ\barΛ $

Utilizing $2712.4 \pm 14.3$ million $ψ(3686)$ events accumulated by the BESIII experiment, we perform a partial wave analysis of $ψ(3686)\rightarrowγχ_{cJ}\rightarrowγΛ\barΛ$ decay ($J=0,1,2$). The ratio of the helicity amplitudes with same (++) and opposite (+-) helicity for $χ_{c2}\rightarrowΛ\barΛ$ decay is determined for the first time to be $R_{χ_{c2}}=0.575 \pm 0.048 \pm 0.018 $, with a relative phase angle $ΔΦ_{χ_{c2}} = 0.37 \pm 0.15 \pm 0.05 $~rad. The parameters of the angular distribution of $χ_{c2}$ are determined to be $α_{χ_{c2}} = -0.211 \pm 0.100 \pm 0.050 $ and $β_{χ_{c2}} = -0.039 \pm 0.089 \pm 0.033 $, based on the distribution $dN / d\cosθ= 1 + α_{χ_{c2}} \cos^2θ+ β_{χ_{c2}} \cos^4θ$. The width of $χ_{c0}$ is determined to be $12.31 \pm 0.26 \pm 0.12 $~MeV. Additionally, the branching fractions for $χ_{cJ} \rightarrow Λ\barΛ$ are measured to be $(3.662 \pm 0.048 \pm 0.111) \times 10^{-4}$, $(1.182 \pm 0.026 \pm 0.042) \times 10^{-4}$, and $(1.704 \pm 0.035 \pm 0.057) \times 10^{-4}$ for $χ_{c0}$, $χ_{c1}$ and $χ_{c2}$, respectively, where the first uncertainty is statistical and the second systematic.

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arXiv2026

First Measurement of the Absolute Branching Fraction of $η_c \to γγ$

We apply a tag-and-probe method to precisely measure the absolute branching fraction of the decay $η_c \to γγ$ with the BESIII experiment at BEPCII. Starting with a large initial sample of $2712.4\pm 14.3$ million $ψ(3686)$ events, a sample of 0.16 million $η_c$ events are tagged via the golden channel $ψ(3686)\to π^0 h_c$, $h_c\to γη_c$, effectively avoiding interference effects. The absolute branching fraction of $η_c \to γγ$ is measured for the first time to be $\mathcal{B}(η_c \to γγ) = (2.45 \pm 0.48_{\rm stat.} \pm 0.09_{\rm syst.}) \times 10^{-4}$. Using the world average value of the total width of the $η_c$, the partial decay width of $η_c \to γγ$ is calculated to be $Γ(η_c \to γγ) = (7.48 \pm 1.48_{\rm stat.} \pm 0.30_{\rm syst.})~{\rm keV}$.

hep-ex↗