arXiv subjects

Y. H. Fan

Publications and source records attributed to Y. H. Fan.

At least 199 records · Page 11Linked to original sources

arXiv2025

Measurement of the $η$ transition form factor through $η' \rightarrow π^+π^-η$ decay

Based on a sample of $(1.0087\pm0.0044)\times10^{10}$ $J/ψ$ events collected at BESIII, the transition form factor of the $η$ meson is extracted by analyzing $J/ψ\toγη',~η'\toπ^+π^-η,~η\toγl^+l^-$ ($l$=$e$, $μ$) events. The measured slope of the transition form factor is $Λ^{-2}=1.645\pm0.093_{\rm stat.}\pm {0.024_{\rm sys.}}$ (GeV/$c^2$)$^{-2}$ for the di-electron channel and $Λ^{-2}=1.645\pm0.343_{\rm stat.}\pm0.017_{\rm sys.}$ (GeV/$c^2$)$^{-2}$ for the di-muon channel. The branching fractions for $η\rightarrowγe^+e^-$ and $η\rightarrowγμ^+μ^-$ are measured to be $\mathcal{B}(η\toγe^+e^-)=(6.79\pm0.04_{\rm stat.}\pm0.36_{\rm sys.})\times 10^{-3}$ and $\mathcal{B}(η\toγμ^+μ^-)=(2.97\pm0.11_{\rm stat.}\pm0.07_{\rm sys.})\times 10^{-4}$. By combining with the results based on the $J/ψ\toγη,~η\toγe^+e^-$ events from the previous BESIII measurement, we determine $Λ^{-2}=1.707\pm0.076_{\rm stat.}\pm0.029_{\rm sys.}$ (GeV/$c^2$)$^{-2}$ and $\mathcal{B}(η\toγe^+e^-)=(6.93\pm0.28_{\rm tot.})\times 10^{-3}$. In addition, we search for the dark photon ($A'$) using the combined events. No significant signal is observed, and the upper limits on $\mathcal{B}(η\toγA',~A'\to e^+e^-)$ are set at 90\% confidence level for different $A'$ mass hypotheses.

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arXiv2025

First observation of quantum correlations in $e^+e^-\to XD\bar{D}$ and $C$-even constrained $D\bar{D}$ pairs

The study of meson pairs produced with quantum correlations gives direct access to parameters that are challenging to measure in other systems. In this Letter, the existence of quantum correlations due to charge-conjugation symmetry $C$ are demonstrated in $D\bar{D}$ pairs produced through the processes $e^+e^-\to D\bar{D}$, $e^+e^- \to D^{*}\bar{D}$, and $e^+e^- \to D^{*} \bar{D}^*$, where the lack of charge superscripts refers to an admixture of neutral-charm-meson particle and antiparticle states, using $7.13 \text{ fb}^{-1}$ of $e^+e^-$ collision data collected by the BESIII experiment between center-of-mass energies of $4.13-4.23 \text{ GeV}$. Processes with either $C$-even or $C$-odd constraints are identified and separated. A procedure is presented that harnesses the entangled production process to enable measurements of $D^0$-meson hadronic parameters. This study provides the first confirmation of quantum correlations in $e^+e^-\to X D\bar{D}$ processes and the first observation of a $C$-even constrained $D\bar{D}$ system. The procedure is applied to measure $δ^{D}_{Kπ}$, the strong phase between the $D^0\to K^-π^+$ and $\bar{D}^0\to K^-π^+$ decay amplitudes, which results in the determination of $δ^{D}_{Kπ}=\left(192.8^{+11.0 + 1.9}_{-12.4 -2.4}\right)^\circ$. The potential for measurements of other hadronic decay parameters and charm mixing with these and future datasets is also discussed.

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arXiv2025

A novel measurement of the strong-phase difference between $D^0\to K^-π^+$ and $\bar{D}^0\to K^-π^+$ decays using $C$-even and $C$-odd quantum-correlated $D\bar{D}$ pairs

A novel measurement technique of strong-phase differences between the decay amplitudes of $D^0$ and $\bar{D}^0$ mesons is introduced which exploits quantum-correlated $D\bar{D}$ pairs produced by $e^+e^-$ collisions at energies above the $ψ(3770)$ production threshold, where $D\bar{D}$ pairs are produced in both even and odd eigenstates of the charge-conjugation symmetry. Employing this technique, the first determination of a $D^0$-$\bar{D^0}$ relative strong phase is reported with such data samples. The strong-phase difference between $D^0\to K^-π^+$ and $\bar{D}^0\to K^-π^+$ decays, $δ^{D}_{Kπ}$, is measured to be $δ^{D}_{Kπ}=\left(192.8^{+11.0 + 1.9}_{-12.4 -2.4}\right)^\circ$, using a dataset corresponding to an integrated luminosity of 7.13 $\text{fb}^{-1}$ collected at center-of-mass energies between $4.13-4.23 \text{ GeV}$ by the BESIII experiment.

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arXiv2025

Search for $η_{1}(1855)$ in $χ_{cJ}\toηηη^{\prime}$ decays

Based on a sample of $2.7\times10^{9}$ $ψ(3686)$ events collected by the BESIII detector operating at the BEPCII collider, an analysis of the decay $ψ(3686)\toγχ_{cJ}, χ_{cJ}\toηηη^{\prime}$ is performed. The decay modes $χ_{c1}$ and $χ_{c2}\toηηη^{\prime}$ are observed for the first time, and their corresponding branching fractions are determined to be $\mathcal{B}(χ_{c1}\toηηη^{\prime}) = (1.40\, \pm 0.13\, (\text{stat.}) \pm 0.09\, (\text{sys.})) \times 10^{-4}$ and $\mathcal{B}(χ_{c2}\toηηη^{\prime}) = (4.18\, \pm 0.84\, (\text{stat.}) \pm 0.48\, (\text{sys.})) \times 10^{-5}$. An upper limit on the branching fraction of $χ_{c0}\toηηη^{\prime}$ is set as $2.59 \times 10^{-5}$ at 90\% confidence level (CL). A partial wave analysis (PWA) of the decay $χ_{c1}\toηηη^{\prime}$ is performed to search for the $1^{-+}$ exotic state $η_1(1855)$. The PWA result indicates that the structure in the $ηη^{\prime}$ mass spectrum is mainly attributed to the $f_0(1500)$, while in the $ηη$ mass spectrum, it is primarily the $0^{++}$ phase space. The upper limit of $\mathcal{B}(χ_{c1}\toη_{1}(1855)η) \cdot \mathcal{B}(η_{1}(1855)\toηη^{\prime})< 9.79 \times 10^{-5}$ is set based on the PWA at 90\% CL.

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arXiv2025

Search for $e^+e^-\to K_S^0 K_S^0 h_c$

Using $e^+e^-$ collision data at 13 center-of-mass energies ranging from 4.600 to 4.950 GeV collected with the BESIII detector, we search for the unmeasured $e^+e^-\to K_S^0 K_S^0 h_c$ process . No significant signal is observed, and the upper limits of the Born cross sections at each center-of-mass energy are presented.

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arXiv2025

Observation of the $W$-annihilation process $D_s^+ \to ωρ^+$ and measurement of $D_s^+ \to ϕρ^+$ in $D^+_s\to π^+π^+π^-π^0π^0$ decays

We present the first amplitude analysis and branching fraction measurement of the decay $D^+_s\to π^+π^+π^-π^0π^0$, using $e^+e^-$ collision data collected with the BESIII detector at center-of-mass energies between 4.128 and 4.226 GeV corresponding to an integrated luminosity of 7.33 fb$^{-1}$, and report the first observation of the pure $W$-annihilation decay $D_s^+ \to ωρ^+$ with a branching fraction of $(0.99\pm0.08_{\rm stat}{\ ^{+0.05}_{-0.07}}_{\rm syst})\%$. %The absolute branching fraction is measured to be $(0.99\pm0.08_{\rm stat}\pm0.07_{\rm syst})\%$. In comparison to the low significance of the $\mathcal{D}$ wave in the decay $D_s^+ \to ϕρ^+$, the dominance of the $\mathcal{D}$ wave over the $\mathcal{S}$ and $\mathcal{P}$ waves, with a fraction of $(51.85\pm7.28_{\rm stat}{\ ^{+4.83}_{-7.90}}_{\rm syst})\%$ observed in the decay $D_s^+ \to ωρ^+$, provides crucial information for the``polarization puzzle", as well as for the understanding of charm meson decays. The branching fraction of $D^+_s\to π^+π^+π^-π^0π^0$ is measured to be ($4.41\pm0.15_{\rm stat}\pm0.13_{\rm syst}$)\%. Moreover, the branching fraction of $D_s^+ \to ϕρ^+$ is measured to be $(3.98\pm0.33_{\rm stat}{\ ^{+0.21}_{-0.19}}_{\rm syst})\%$, and the $R_ϕ= {\mathcal{B}(ϕ\toπ^+π^-π^0)}/{\mathcal{B}(ϕ\to K^+K^-)}$ is determined to be $(0.222\pm0.019_{\rm stat}{\ ^{+0.016}_{-0.016}}_{\rm syst}$), which is consistent with the previous measurement based on charm meson decays, but deviates from the results from $e^+e^-$ annihilation and $K$-$N$ scattering experiments by more than 3$σ$.

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arXiv2025

Observation of $χ_{cJ}\to 3K_S^0K^\pmπ^\mp$

By analyzing $(2712.4\pm14.3)\times10^6$ $ψ(3686)$ events collected with the BESIII detector operating at the BEPCII collider, the decays $χ_{c0,1,2} \to 3K_S^0K^\pmπ^\mp$ are observed for the first time with statistical significances greater than $10σ$. The branching fractions of these decays are determined to be $\mathcal{B}(χ_{c0}\to 3K_S^0K^\pmπ^\mp )=(7.95\pm0.50\pm0.65)\times10^{-5},$ $\mathcal{B}(χ_{c1}\to 3K_S^0K^\pmπ^\mp)=(2.62\pm0.08\pm0.19)\times10^{-4},$ and $\mathcal{B}(χ_{c2}\to 3K_S^0K^\pmπ^\mp)=(1.72\pm0.07\pm0.15)\times10^{-4},$ where the first uncertainties are statistical and the second systematic.

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arXiv2025

Observation of an Altered $a_{0}(980)$ Line-shape in $D^{+} \rightarrow π^{+}ηη$ due to the Triangle Loop Rescattering Effect

Using 20.3~${\rm fb}^{-1}$ of $e^{+}e^{-}$ collision data taken with the BESIII detector at the center-of-mass energy 3.773~GeV, we report the first amplitude analysis of the hadronic decay $D^{+} \rightarrow π^{+}ηη$. The intermediate process $D^{+} \to a_{0}(980)^{+}η, a_{0}(980)^{+} \to π^{+}η$ is observed and is found to be the only component and its branching fraction is measured to be $(3.67\pm0.12_{\mathrm{stat.}}\pm 0.06_{\mathrm{syst.}})\times 10^{-3}$. Unlike the $a_{0}(980)$ line-shape observed in the decays of charmed mesons to $a_{0}(980)π$ and in the decay $D^{0} \to a_{0}(980)^{-}e^{+}ν_{e}$, where the low-mass side of the $a_0(980)$ is wider than the high-mass side, the $a_{0}(980)$ line-shape in $D^{+} \to a_{0}(980)^{+}η$ is found to be significantly altered, with the high-mass side being wider than the low-mass side. We establish that the $a_0(980)$ line-shape arises from the triangle loop rescattering of $D^+ \to \bar{K}_0^*(1430)^0K^+ \to a_0(980)^+ η$ and $D^+ \to K_0^*(1430)^+\bar{K}^0 \to a_0(980)^+ η$ with a significance of 5.8$σ$. This is the first experimental confirmation of the triangle loop rescattering effect.

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arXiv2025

Measurement of the branching fraction of the decay $J/ψ\to p \bar{p} η$

A high precision measurement of the branching fraction of the decay $J/ψ\to p \bar{p} η$ is performed using $(10 087 \pm 44) \times 10^6$ $J/ψ$ events recorded by the {BESIII} detector at the {BEPCII} storage ring. The branching fractions of the two decays $J/ψ\to p \bar{p} η(η\to γγ)$ and $J/ψ\to p \bar{p} η(η\to π^+ π^- π^0)$ are measured individually to be $\mathcal{B}(J/ψ\to p \bar{p} η(η\to γγ)) = (1.480 \pm 0.001 \pm 0.024)\times\,10^{-3}$ and $\mathcal{B}(J/ψ\to p \bar{p} η(η\to π^+ π^- π^0)) = (1.557 \pm 0.003 \pm 0.038)\times\,10^{-3}$, where the first uncertainties are statistical and the second systematic. Both results are compatible within their uncorrelated systematic uncertainties. The combined result is $\mathcal{B}(J/ψ\to p \bar{p} η)=(1.495 \pm 0.001 \pm 0.023)\times\,10^{-3}$ where the first uncertainty is the combined statistical uncertainty and the second one the combined systematic uncertainty of both analyses, incorporating correlations between them. In addition, the $p \bar{p}$ threshold region is investigated for a potential threshold enhancement, and no evidence for one is observed.

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arXiv2025

Search for the lepton number violation decay $ω\to π^+ π^+ e^-e^- +c.c.$

The lepton number violation decay $ω\to π^+ π^+ e^-e^- +c.c.$ is searched for via $J/ψ\to ωη$ using a data sample of $(1.0087 \pm 0.0044) \times 10^{10}$ $J/ψ$ events collected by the BESIII detector at the BEPCII collider. No significant signal is observed, and the upper limit on the branching fraction of $ω\to π^+ π^+ e^-e^- +c.c.$ at the 90\% confidence level is determined for the first time to be $2.8 \times 10^{-6}$.

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arXiv2025

Measurements of branching fractions of $D^0\to K^- 3π^+2π^-$, $D^0\to K^- 2π^+π^-2π^0$ and $D^+\to K^- 3π^+π^-π^0$

Utilizing $7.9\,\rm fb^{-1}$ of $e^+e^-$ collision data taken with the BESIII detector at the center-of-mass energy of 3.773 GeV, we report the measurements of absolute branching fractions of the hadronic decays $D^0\to K^- 3π^+2π^-$, $D^0\to K^- 2π^+π^-2π^0$ and $D^+\to K^- 3π^+π^-π^0$. The $D^0\to K^- 3π^+2π^-$ decay is measured with improved precision, while the latter two decays are observed with statistical significance higher than $5σ$ for the first time. The absolute branching fractions of these decays are determined to be ${\mathcal B}(D^0\to K^- 3π^+2π^-)=( 1.35\pm 0.23\pm 0.08 )\times 10^{-4}$, ${\mathcal B}(D^0\to K^- 2π^+π^-2π^0)=( 19.0\pm 1.1\pm 1.5)\times 10^{-4}$, and ${\mathcal B}(D^+\to K^- 3π^+π^-π^0)=( 6.57\pm 0.69\pm 0.33)\times 10^{-4}$, where the first uncertainties are statistical and the second systematic.

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arXiv2025

Evidence for Two Excited $Ω^{-}$ Hyperons

Using $e^+e^-$ collision data corresponding to an integrated luminosity of 19,fb$^{-1}$ collected by the BESIII detector at center-of-mass energies ranging from 4.13 to 4.70,GeV, we report the first evidence for a new excited $Ω^{-}$ hyperon, the $Ω(2109)^{-}$, through the process $e^+ e^- \to Ω(2109)^{-} \barΩ^{+} +c.c.$ with a significance of 4.1 $σ$. The mass and width of $Ω(2109)^{-}$ are measured to be $2108.5 \pm 5.2_{\rm stat} \pm 0.9_{\rm syst}\,{\rm MeV}/c^{2}$ and $18.3 \pm 16.4_{\rm stat} \pm 5.7_{\rm syst}\,{\rm MeV}$, respectively. We also present evidence for a new production mechanism for the previously identified $Ω(2012)^-$ via the process $e^+ e^- \to Ω(2012)^{-} \barΩ^{+} +c.c.$ with a significance of 3.5 $σ$.

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arXiv2025

Search for $1^{-+}$ charmonium-like hybrid via $e^{+}e^{-}\rightarrow γη^{(\prime)} η_{c}$ at center-of-mass energies between 4.258 and 4.681 GeV

Using $e^{+}e^{-}$ collision data corresponding to an integrated luminosity of 10.6 fb$^{-1}$ collected at center-of-mass energies between 4.258 and 4.681 GeV with the BESIII detector at the BEPCII collider, we search for the $1^{- +}$ charmonium-like hybrid via $e^{+}e^{-}\rightarrowγηη_{c}$ and $e^{+}e^{-}\rightarrowγη^{\prime}η_{c}$ decays for the first time. No significant signal is observed and the upper limits on the Born cross sections for both processes are set at the 90% confidence level.

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arXiv2025

Updated model-independent measurement of the strong-phase differences between $D^0$ and $\bar{D}^0 \to K^{0}_{S/L}π^+π^-$ decays

The strong-phase differences between $D^0\to K_{S/L}^0π^+π^-$ and $\bar{D}^0\to K_{S/L}^0π^+π^-$ decays are one of the most important inputs in measuring the $C\!P$ violating angle $γ$ via $B^- \to D K^-$ decays. They also play a key role in studies of charm mixing and indirect $C\!P$ violation. In this paper, the strong-phase differences are determined in a model-independent way with quantum-correlated $D^0$-$\bar{D}^0$ decays from 7.93 fb$^{-1}$ of $e^+e^-$ annihilation data at $\sqrt{s}$=3.773 GeV by the BESIII experiment. These results are the most precise to date and are expected to significantly reduce associated uncertainties in determining the $C\!P$ violating angle $γ$ and related charm mixing parameters.

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arXiv2025

Observation of $D\to \bar{K}_{1}(1270)μ^+ν_μ$ and test of lepton flavor universality with $D\to \bar{K}_1(1270) \ell^{+} ν_{\ell}$

By analyzing 7.93 $\rm fb^{-1}$ of $e^+e^-$ collision data collected at the center-of-mass energy of 3.773 GeV with the BESIII detector operated at the BEPCII collider, we report the observation of the semimuonic decays of $D^+\to \bar K_1(1270)^0μ^+ν_μ$ and $D^0\to K_1(1270)^-μ^+ν_μ$ with statistical significances of $12.5σ$ and $6.0σ$, respectively. Their decay branching fractions are determined to be ${\mathcal B}[D^{+}\to \bar{K}_1(1270)^0 μ^{+}ν_μ]=(2.36\pm0.20^{+0.18}_{-0.27}\pm 0.48)\times10^{-3}$ and ${\mathcal B}[D^{0}\to K_1(1270)^{-} μ^{+}ν_μ]=(0.78\pm0.11^{+0.05}_{-0.09}\pm 0.15)\times10^{-3}$, where the first and second uncertainties are statistical and systematic, respectively, and the third originates from the input branching fraction of $\bar K_{1}(1270)^0\to K^- π^+π^0$ or $K_1(1270)^-\to K^-π^+π^-$. Combining our branching fractions with the previous measurements of ${\mathcal B}[D^+\to \bar K_1(1270)^0e^+ν_{e}]$ and ${\mathcal B}[D^0\to K_1(1270)^-e^+ν_{e}]$, we determine the branching fraction ratios to be ${\mathcal B}[D^+\to \bar K_1(1270)^0μ^+ν_μ]/{\mathcal B}[D^+\to \bar K_1(1270)^0e^+ν_{e}]=1.03 \pm 0.14 \substack{+0.11\\-0.15}$ and ${\mathcal B}[D^0\to K_1(1270)^-μ^+ν_μ]/{\mathcal B}[D^0\to K_1(1270)^-e^+ν_{e}]=0.74\pm 0.13 \substack{+0.08\\-0.13}$. Using the branching fractions measured in this work and the world-average lifetimes of the $D^+$ and $D^0$ mesons, we determine the semimuonic partial decay width ratio to be $Γ[D^+\to \bar K_1(1270)^0 μ^+ν_μ]/Γ[D^0\to K_1(1270)^- μ^+ν_μ]=1.22\pm 0.10\substack{+0.06\\-0.09}$, which is consistent with unity as predicted by isospin conservation.

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arXiv2025

Precise measurement of the form factors in $D^0\rightarrow K^(892)^-μ^+ν_μ$ and test of lepton universality with $D^0\rightarrow K^(892)^-\ell^+ν_{\ell}$ decays

We report a study of the semileptonic decay $D^0 \rightarrow \bar{K}^0π^-μ^+ν_μ$ based on a sample of $7.9~\mathrm{fb}^{-1}$ of $e^+e^-$ annihilation data collected at a center-of-mass energy of 3.773~GeV with the BESIII detector at the BEPCII collider. The branching fraction of the decay is measured for the first time to be $\mathcal{B}(D^0\rightarrow \bar{K}^0π^-μ^+ν_μ) = (1.373 \pm 0.020_{\rm stat} \pm 0.023_{\rm syst})\%$, where the first uncertainty is statistical and the second is systematic. Based on the investigation of the decay dynamics, we find that the decay is dominated by the $K^{*}(892)^-$ resonance with the branching fraction measured to be $\mathcal{B}(D^0\rightarrow K^{*}(892)^-μ^+ν_μ) = (1.948 \pm 0.033_{\rm stat} \pm 0.036_{\rm syst})\%$. We also determine the hadronic form factors for the $D^0\rightarrow K^{*}(892)^-μ^+ν_μ$ decay to be $r_{V} = V(0)/A_1(0) = 1.46 \pm 0.11_{\rm stat} \pm 0.04_{\rm syst}$, $r_{2} = A_2(0)/A_1(0) = 0.71 \pm 0.08_{\rm stat} \pm 0.03_{\rm syst}$, and $A_1(0)=0.609 \pm 0.008_{\rm stat} \pm 0.008_{\rm syst}$, where $V(0)$ is the vector form factor and $A_{1,2}(0)$ are the axial form factors evaluated at $q^2=0$. The $A_1(0)$ is measured for the first time in $D^0\rightarrow K^{*}(892)^-μ^+ν_μ$ decay. Averaging the form-factor parameters that we reported previously in $D^0\rightarrow K^*(892)^-(\rightarrow \bar{K}^0π^-)e^+ν_{e}$ and $D^0\rightarrow K^*(892)^-(\rightarrow K^-π^0)μ^+ν_μ$ decays, we obtain $r_{V}=1.456\pm0.040_{\rm stat}\pm0.016_{\rm syst}$, $r_{2}=0.715\pm0.031_{\rm stat}\pm0.014_{\rm stat}$, and $A_1(0)=0.614\pm0.005_{\rm stat}\pm0.004_{\rm syst}$. This is the most precise determination of the form-factor parameters to date measured in $D\rightarrow K^*(892)$ transition, which provide the most stringent test on various theoretical models.

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arXiv2025

Search for the baryon and lepton number violating decay $J/ψ\to pe^-$ + c.c

Based on $(2712.4\pm 14.3) \times 10^{6} $ ${ψ(3686)}$ events collected by the BESIII detector operating at the BEPCII storage ring, we perform a search for the baryon- and lepton-number violating decay $J/ψ\to pe^{-}+c.c.$ via $ψ(3686) \to π^{+}π^{-}J/ψ$. No significant signal is found. An upper limit on the branching fraction of $\mathcal{B}(J/ψ\to p e^{-}+ c.c.) < 3.1 \times 10^{-8}$ at 90\% confidence level.

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arXiv2025

Observation of the charmonium decay $η_c\toγγ$ in $J/ψ\toγη_c$

Using $(2712.4\pm14.3)\times10^{6}$ $ψ(3686)$ events collected with the BESIII detector at the BEPCII collider, the decay $η_c\toγγ$ in $J/ψ\toγη_c$ is observed. We determine the product branching fraction $\mathcal{B}(J/ψ\toγη_c)\times\mathcal{B}(η_c\toγγ)=(5.23\pm0.26_{\rm{stat.}}\pm0.30_{\rm{syst.}})\times10^{-6}$. This result is consistent with the LQCD calculation $(5.34\pm0.16)\times10^{-6}$ from HPQCD in 2023. By using the world-average values of $\mathcal{B}(J/ψ\toγη_c)$ and the total decay width of $η_c$, the partial decay width $Γ(η_c\toγγ)$ is determined to be $(11.30\pm0.56_{\rm{stat.}}\pm0.66_{\rm{syst.}}\pm1.14_{\rm{ref.}})~\rm{keV}$, which deviates from the corresponding world-average value by $3.4σ$.

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