arXiv subjects

J. C. Cheng

Publications and source records attributed to J. C. Cheng.

At least 19 recordsLinked to original sources

arXiv2026

Measurement of Branching Fraction and Transition Magnetic Moment of the Hyperon Dalitz Decay $\Sigma^0 \rightarrow \Lambda e^+e^-$

Based on a data sample of 10 billion $J/\psi$ events collected with the BESIII detector operating at the BEPCII collider, the Dalitz decay $\Sigma^0 \rightarrow \Lambda e^+e^-$ is studied experimentally for the first time. The $\Sigma^0$ hyperons are produced through the process $J/\psi \rightarrow \Sigma^0\bar{\Sigma}^0$ and analyzed using a double-tag method. The absolute branching fraction is measured to be $\mathcal{B}(\Sigma^0 \rightarrow \Lambda e^+e^-) = (6.34 \pm 0.25_{\rm stat.} \pm 0.23_{\rm syst.}) \times 10^{-3}$. This result shows a $2\sigma$ discrepancy from the theoretical calculation quoted in the PDG, where the uncertainties are statistical and systematic, respectively. In addition to the branching fraction, the transition magnetic moment $\mu$ is determined to be $(1.74 \pm 0.03_{\rm stat.} \pm 0.09_{\rm syst.})\,\mu_N$, where $\mu_N=e/(2m_p)$ represents the nucleon magnetic moment, providing valuable insight into the intrinsic structure of the $\Sigma^0$ hyperon.

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arXiv2026

Measurement of branching fractions of $D^+_s\to K^0_SK^0_S \pi^+\pi^0$ and $D^+_s\to K^0_S K^+\pi^0\pi^0$

By analyzing $e^+e^-$ collision data corresponding to an integrated luminosity of 7.33~fb$^{-1}$ collected with the BESIII detector at center-of-mass energies ranging from 4.128 to 4.226~GeV, we report the observations of the hadronic decays $D^+_s\to K^0_SK^0_S\pi^+\pi^0$ and $D^+_s\to K^0_S K^+\pi^0\pi^0$. Their decay branching fractions are determined to be ${\mathcal B}(D^+_s\to K^0_SK^0_S \pi^+\pi^0)=(4.08\pm0.46_{\rm stat}\pm0.45_{\rm syst})\times 10^{-3}$ and ${\mathcal B}(D^+_s\to K^0_S K^+\pi^0\pi^0)=(3.32\pm0.64_{\rm stat}\pm0.31_{\rm syst})\times 10^{-3}$, where the first uncertainties are statistical and the second are systematic.

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arXiv2026

Search for the radiative decays $D^0\to \gamma \bar K_1(1270)^0$ and $D^+\to \gamma K_1(1270)^+$

A search for the radiative decays $D^0\to \gamma \bar K_1(1270)^0$ and $D^+\to \gamma K_1(1270)^+$ is conducted using $20.3~\mathrm{fb}^{-1}$ of $e^+e^-$ annihilation data collected at the center-of-mass energy $\sqrt{s}=3.773$ GeV by the BESIII detector operating at the BEPCII collider. No significant signals are observed, and upper limits on the branching fractions of $D^0\to \gamma \bar K_1(1270)^0$ and $D^+\to \gamma K_1(1270)^+$ at 90\% confidence level are determined to be $7.7\times10^{-4}$ and $3.9\times10^{-5}$, respectively. This represents the first test of the Vector Meson Dominance mechanism in the radiative decays of charmed mesons to axial-vector mesons.

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arXiv2026

Amplitude Analysis of Singly Cabibbo-Suppressed Decay $\Lambda^{+}_{c}\to p K^{+} K^{-}$

Using a sample of $e^{+}e^{-}$ annihilation data corresponding to an integrated luminosity of 4.4 $\rm{fb}^{-1}$ collected with the BESIII detector at the BEPCII collider and produced at center-of-mass energies from $4600$ to $4698~\rm{MeV}$, an amplitude analysis is performed of the singly Cabibbo-suppressed decay $\Lambda^{+}_{c}\to pK^{+}K^{-}$. The branching fractions of $\Lambda^{+}_{c}\to p\phi(1020)$, $pf_{0}(980)$, $\Lambda(1405)K^{+}$, and $\Lambda(1670)K^{+}$ are measured, where the latter two modes are decays that are observed for the first time. At the same time, with the detection efficiency based on the results of the amplitude analysis, the branching fraction of $\Lambda^{+}_{c}\to pK^{+}K^{-}$ is updated to be $(9.94\pm0.65_{\text{stat.}}\pm0.50_{\text{syst.}})\times10^{-4}$, which is consistent with the current world average value within one standard deviation. The result supersedes the previous BESIII measurement with precision improved by approximately a factor of 1.5.

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arXiv2026

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

We report a study of the semileptonic decays $D^0 \rightarrow \bar{K}^0\pi^-\ell^+\nu_{\ell}$ (where $\ell=e,~\mu$) 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 $D^0 \rightarrow \bar{K}^0\pi^-\ell^+\nu_{\ell}$ decays, a $\mathcal{D}-$wave component of $D^0\rightarrow K_2^*(1430)^-\ell^+\nu_{\ell}$ is observed for the first time with a statistical significance of $8.0\sigma$, 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 $\mathcal{B}(D^0\rightarrow K^{*}(892)^-e^+\nu_{e}) = (2.043 \pm 0.018_{\rm stat} \pm 0.012_{\rm syst})\%$ and $\mathcal{B}(D^0\rightarrow K^{*}(892)^-\mu^+\nu_{\mu}) = (1.964 \pm 0.018_{\rm stat} \pm 0.012_{\rm syst})\%$, 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 $\bar{K}^0\pi^-$ system.

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arXiv2026

First Amplitude Analysis of $D^0\rightarrow K^-\pi^0e^+\nu_e$ and Observation of $D^0\rightarrow K^*_2(1430)^-e^+\nu_e$

We present the first amplitude analysis of the semileptonic decay $D^0\to K^-\pi^0 e^{+}\nu_{e}$ by analyzing $e^+e^-$ annihilation data corresponding to an integrated luminosity of 20.3 fb$^{-1}$ collected at the center-of-mass energy of 3.773 GeV with the BESIII detector. A tiny $\mathcal{D}$-wave component of the $K^*_2(1430)^-$ accounting for $(0.16 \pm 0.05_{\rm stat} \pm 0.02_{\rm syst})\%$ of the $K^-\pi^0$ is observed for the first time with a significance of $7.9\sigma$ in addition to the dominant $\mathcal{P}$-wave component of $K^*(892)^-$ and the sub-dominant $K^-\pi^0$ $\mathcal{S}$-wave. The hadronic form factors of the $D^0 \to K^*(892)^-$ transition are measured precisely as $r_V=V(0)/A_1(0)=1.41 \pm 0.05_{\rm stat} \pm 0.01_{\rm syst}$ and $r_2=A_2(0)/A_1(0)=0.77 \pm 0.04_{\rm stat} \pm 0.02_{\rm syst}$. The branching fraction of $D^0\to K^*(892)^-e^+\nu_e$ with $K^*(892)^-\to K^-\pi^0$ is measured to be $(7.403\pm0.061_{\rm stat.} \pm 0.048_{\rm syst.})\times10^{-3}$. Combining the measurements of the $D^0\to K^*(892)^-(K^*(892)^-\to K^-\pi^0)\ell^+ \nu_\ell$, lepton flavor universality is tested by the ratio $\mathcal{R}_{\rm LFU}=\mathcal{B}(D^0\to K^*(892)^-\mu^+ \nu_\mu)/\mathcal{B}(D^0\to K^*(892)^-e^+\nu_e)=0.928\pm0.020_{\rm stat}\pm0.012_{\rm syst}$ with unprecedented precision; no violation is found. Furthermore, isospin symmetry in the decay $K^*(892) \to K\pi$ is tested by $\mathcal R_{K^{*-}} =\mathcal{B}(K^*(892)^-\to K^- \pi^0)/\mathcal{B}(K^*(892)^-\to K_S^0 \pi^-)= 1.09\pm0.02_{\rm stat}\pm0.02_{\rm syst}$ for the first time using the previous measurement of $D^0\to K^*(892)^-e^+\nu_e$ with $K^*(892)^-\to K^0_S\pi^-$. Finally, the phase shift of the $K\pi$ \wv{S} is extracted in a model-independent way, which sheds light on the nature of the lightest strange scalar meson, the $K^*_0(700)$.

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arXiv2026

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

Improved measurements of the coherence factors and strong-phase differences in $D\to K^-\pi^+\pi^+\pi^-$ and $D\to K^-\pi^+\pi^0$ 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 $\gamma$ of the Cabibbo-Kobayashi-Maskawa Unitarity Triangle in the LHCb and Belle II experiments. The coherence factors are determined to be $R_{K3\pi}=0.51\pm0.04$ and $R_{K\pi\pi^0}=0.75\pm0.03$, and the strong-phase differences are $\delta_D^{K3\pi}=\left(182^{+14}_{-13}\right)^\circ$ and $\delta_D^{K\pi\pi^0}=\left(209^{+7}_{-8}\right)^\circ$, where the uncertainties include both statistical and systematic contributions. For $D\to K^-\pi^+\pi^+\pi^-$, the parameters have been further determined in four phase-space bins with improved precision compared to the previous BESIII results. The uncertainty on future $\gamma$ measurements from the knowledge of $D\to K^-\pi^+\pi^+\pi^-$ parameters is expected to be reduced to approximately 3.5$^\circ$.

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arXiv2026

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

Using a data sample of $(2712.4\pm14.3)\times10^6\ \psi(3686)$ events collected with the BESIII detector, a partial-wave analysis of $\psi(3686)\to\bar{p}K^+\Sigma^0+c.c.$ is performed. A new excited $\Sigma$ baryon state is observed with a statistical significance of $11.9\sigma$, 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 $\psi(3686)\to\bar{\Sigma}(2330)^0\Sigma^0+c.c.$ is determined to be $(4.47\pm0.58\pm1.52)\times10^{-6}$. In addition, the branching fraction of $\psi(3686)\to\bar{p}K^+\Sigma^0+c.c.$ 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

Search for sub-GeV dark particles in $\eta\to\pi^0+\rm{invisible}$ decay

Using (10087$\pm$44)$\times$10$^{6}$ $J/\psi$ events collected with the BESIII detector at the BEPCII collider at the center-of-mass energy of $\sqrt{s}=3.097~\rm{GeV}$, we report the first search for $\eta\to\pi^0S\to\pi^0\chi\bar{\chi}$ with $S$ denotes an on-shell dark scalar boson and $\chi$ an invisible dark matter particle. No significant signals are observed with $S$ mass ranging from 0 to 400 $\rm{MeV}/c^2$. The upper limits on the branching fractions and the new physics coupling strengths between $S$ and quarks are set to be $(1.8\sim5.5)\times10^{-5}$ and $(1.3\sim3.2)\times10^{-5}$ at the 90% confidence level, respectively. The constraints on the dark-matter-nucleon scattering cross section is improved by approximately 5 orders of magnitude over previous dark-matter-nucleon scattering experiments, providing unique insights into sub-GeV dark matter.

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arXiv2026

First Observation of $D^{0(+)}\to \bar K\omega e^+\nu_e$ and Determination of the Branching Fraction of $\bar K_1(1270)\to \bar K \omega$

Using 20.3~fb$^{-1}$ of $e^+e^-$ annihilation data collected at a center-of-mass energy of 3.773~GeV with the BESIII detector, we report the first observation of the semileptonic decays \mbox{$D^0\to K^-\omega e^+\nu_e$} and \mbox{$D^+\to K_S^0\omega e^+\nu_e$} with significances of $8.0\sigma$ and $5.8\sigma$, respectively. Their decay branching fractions are measured to be ${\cal B}(D^0\to K^-\omega e^+\nu_e)=(9.4^{+2.0}_{-1.8}\pm 0.6)\times10^{-5}$ and ${\cal B}(D^+\to K_S^0\omega e^+\nu_e)=(8.0^{+2.4}_{-2.1}\pm 0.7)\times10^{-5}$. Combining these with the latest measurements of $D^{0(+)}\to K^-\pi^+\pi^{-(0)} e^+\nu_e$ and assuming $\bar{K}_1(1270)$ to be the sole mediating resonance in all processes, the branching ratios are determined to be $\frac{\Gamma(K_1(1270)^-\to K^-\pi^+\pi^-)}{\Gamma(K_1(1270)^-\to K^-\omega)} = 3.4^{+0.8}_{-0.7} \pm 0.3$ and $\frac{\Gamma(\bar{K}_1(1270)^0\to K^-\pi^+\pi^0)}{\Gamma(\bar{K}_1(1270)^0\to \bar{K}^0\omega)} = 7.9^{+2.4}_{-2.1} \pm 0.7$. The combined branching fraction is determined to be $\mathcal B(\bar{K}_1(1270)\to \bar{K}\omega) = (8.4\pm 1.4 \pm 0.5)\%$, which is the most precise measurement from a collider experiment. Furthermore, %based on the $\bar{K}\pi^+\pi^-\pi^0$ invariant mass spectra, for the first time based on a single vector-pseudoscalar decay channel, the $\bar{K}_1(1270)$ mass is measured to be $(1336 \pm 9 \pm 2)$~MeV/$c^2$, providing unique experimental support for the two-pole structure of the $\bar{K}_1(1270)$ resonance. The first uncertainties are statistical, and the second are systematic.

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arXiv2026

Cross section measurement of $e^{+}e^{-}\rightarrow \pi^{0}\pi^{0}\psi(3686)$ from $\sqrt{s}=$ 4.008 GeV to 4.951 GeV

Using data samples with a total integrated luminosity of $22.1~\rm fb^{-1}$ at center-of-mass energies between 4.008 and 4.951~GeV collected with the BESIII detector, the cross sections of $e^{+}e^{-}\rightarrow \pi^{0}\pi^{0}\psi(3686)$ process are measured. The obtained cross sections are found to be approximately one-half of those of $e^{+}e^{-}\rightarrow \pi^{+}\pi^{-}\psi(3686)$, consistent with the isospin symmetry expectation. A coherent fit to the dressed cross sections is performed, with the $Y(4230)$~parameters fixed at the values measured in $e^{+}e^{-}\rightarrow \pi^{+}\pi^{-}\psi(3686)$. The significances of the $Y(4390)$ and $Y(4660)$ are both larger than $5\sigma$, and their masses and widths are consistent with the previous measurement in the $e^{+}e^{-}\rightarrow \pi^{+}\pi^{-}\psi(3686)$ process.

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arXiv2025

Cross sections measurement of $e^+e^-\to \Xi(1530)^0\bar\Xi^0 + c.c.$ and search for $\psi(3770)\to\Xi(1530)^0\bar\Xi^0 + c.c.$

Using $e^+e^-$ collision data collected with the BESIII detector corresponding to an integrated luminosity of 44.2 fb$^{-1}$, we measure the Born cross sections for the process $e^+e^- \to \Xi(1530)^{0} \bar{\Xi}^{0} + c.c.$ at forty-eight center-of-mass energies between 3.51 and 4.95 GeV. The potential signal from non-$D\bar{D}$ decays for $\psi(3770)$, i.e. $\psi(3770)\to \Xi(1530)^{0} \bar{\Xi}^{0}+ c.c.$, is investigated by fitting the dressed cross section, no obvious signal is found. The upper limit of $\mathcal{B}(\psi(3770) \to \Xi(1530)^{0} \bar{\Xi}^{0}$) at 90\% confidence level is given.

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arXiv2025

Measurements of the Absolute Branching Fraction of the Semileptonic Decay $\mathbf{\Xi^{-}\rightarrow \Lambda e^- \bar\nu_{e}}$ and the Axial Charge of the $\mathbf\Xi^{-}$

Using $(10087\pm44)\times10^6$ $J/\psi$ events collected with the BESIII detector, we study the semileptonic decay $\Xi^{-}\rightarrow \Lambda e^- \bar\nu_{e}$ for the first time at an electron-positron collider. The absolute branching fraction is determined for the first time to be $(3.60\pm0.40_{\mathrm{stat}}\pm0.10_{\mathrm{syst}})\times10^{-4}$, which is 3.9 standard deviations below the world average. In addition, using an 11-dimensional angular analysis, the axial-vector to vector coupling $g_{av}$ is determined to be $0.18\pm0.07_{\mathrm{stat}}\pm0.02_{\mathrm{syst}}$. These results are used to test various SU(3)-flavour effective models. Under the SU(3)-flavour symmetry limit, the axial charge is found to be $g_A^H = 0.22\pm0.08_{\mathrm{stat}}\pm0.02_{\mathrm{syst}}$. Despite using only 5\% of the statistics of previous experiments, this analysis achieves a comparable precision for the axial charge.

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arXiv2025

Measurements of the branching fractions of $\chi_{cJ}\to \phi\phi\eta, \phi\phi\eta^{\prime}$ and $\phi K^+K^-\eta$

Using a sample of $(2712.4 \pm 14.3)\times 10^6 ~\psi$(3686) events collected by the BESIII detector at the BEPCII collider, we measure the branching fractions of the decays $\chi_{cJ}\to \phi\phi\eta,~\phi\phi\eta^{\prime}$, and~$\phi K^+K^-\eta $ ($J = 0, 1, 2$). The obtained branching fractions are $\mathcal{B}(\chi_{c0} \to \phi\phi\eta) = (7.40 \pm 0.23 \pm 0.55)\times10^{-4}$, $\mathcal{B}(\chi_{c1} \to \phi\phi\eta) = (3.33 \pm 0.14 \pm 0.25)\times10^{-4}$, $\mathcal{B}(\chi_{c2} \to \phi\phi\eta) = (5.46 \pm 0.17 \pm 0.40)\times10^{-4}$, $\mathcal{B}(\chi_{c0} \to \phi\phi\eta^\prime) = (2.96 \pm 0.23 \pm 0.29)\times10^{-4}$, $\mathcal{B}(\chi_{c1} \to \phi\phi\eta^\prime) = (0.69 \pm 0.10 \pm 0.08)\times10^{-4}$, $\mathcal{B}(\chi_{c2} \to \phi\phi\eta^\prime) = (0.65 \pm 0.09 \pm 0.07)\times10^{-4}$, $\mathcal{B}(\chi_{c0} \to \phi K^+K^-\eta) = (1.23 \pm 0.08 \pm 0.10)\times10^{-4}$, $\mathcal{B}(\chi_{c1} \to \phi K^+K^-\eta) = (1.00 \pm 0.07 \pm 0.07)\times10^{-4}$, and $\mathcal{B}(\chi_{c2} \to \phi K^+K^-\eta) = (1.82 \pm 0.09 \pm 0.14)\times10^{-4}$, where $K^+K^-$ is not from the decay of a $\phi$ meson, the first uncertainties are statistical and the second systematic. The branching fractions of $\chi_{cJ}\to \phi\phi\eta$ are measured with precision improved by factors of $1.5-1.9$, and those of $\chi_{cJ}\to \phi\phi\eta^\prime$ and $\phi K^+K^-\eta$ are measured for the first time.

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arXiv2025

Amplitude Analysis and Branching Fraction Measurement of $D^+ \to \pi^+\pi^0\pi^0$

We present the first amplitude analysis of the hadronic decay $D^+\to\pi^+\pi^0\pi^0$, using $e^{+}e^{-}$ collision data collected with the BESIII detector at a center-of-mass energy of 3.773~GeV, corresponding to an integrated luminosity of 20.3~fb$^{-1}$. The fit fractions of the intermediate processes are measured, in which the $D^+ \to \rho(770)^+\pi^0$ component is found to be dominant with a branching fraction of $(3.08\kern0.15em\pm\kern0.15em0.10_{\rm stat.}\pm0.05_{\rm syst.})\times10^{-3}$. Based on the amplitude analysis, the branching fraction of $D^+ \to \pi^+\pi^0\pi^0$ is measured to be $(4.84\kern0.1em\pm\kern0.1em0.05_{\rm stat.}\kern0.1em\pm\kern0.1em0.05_{\rm syst.})\times10^{-3}$. In addition, the CP asymmetries, both for specific amplitudes and integrated over the entire phase space, are measured.

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arXiv2025

Measurement of the branching fraction of $\eta \to \mu^+ \mu^-$ and search for $\eta \to e^+ e^-$

We analyze the decay of $\eta\rightarrow \ell^+\ell^-(\ell=e, \mu)$ via $J/\psi\rightarrow\gamma\eta'$ and $\eta'\rightarrow\pi^+\pi^-\eta$, based on (10087 $\pm$ 44) $\times$ 10$^{6}$ $J/\psi$ events collected with the BESIII detector at the BEPCII storage rings. The branching fraction of $\eta\rightarrow\mu^+ \mu^-$ 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 $\eta\to e^+e^-$ signal is observed in the $e^+ e^-$ invariant mass spectrum, and an improved upper limit of ${\cal B}(\eta \to e^+ e^-) < 2.2 \times 10^{-7}$ is set at 90\% confidence level.

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arXiv2025

Experimental study of the reaction $\Xi^{0}n\rightarrow\Lambda\Lambda X$ using $\Xi^{0}$-nucleus scattering

Using $(10087\pm44)\times10^{6}$$J/\psi$ 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 $\Xi^0n\rightarrow\Lambda\Lambda X$, 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 $\Xi^0 n \rightarrow \Lambda\Lambda$ and $\Xi^{0}n\rightarrow\Lambda\Sigma^0\rightarrow\Lambda\Lambda\gamma$. The $\Xi^0$ comes from the decay of $J/\psi\rightarrow\Xi^0\bar{\Xi}^0$, 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$\sigma$. The cross section for the reaction $\Xi^0+{^9\rm{Be}}\rightarrow\Lambda+\Lambda+X$ is measured to be $(43.6\pm10.5_{\text{stat}}\pm11.1_{\text{syst}})$ mb at $P_{\Xi^0}\approx0.818$ GeV/$c$, where the first uncertainty is statistical and the second systematic. No significant $H$-dibaryon signal is observed in the $\Lambda\Lambda$ final state.

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arXiv2025

Search for the charmonium weak decay $J/\psi\to\bar{D}^0\bar{K}^{*0}+{\rm c.c.}$

Based on a sample of $(10087\pm44)\times10^6$ $J/\psi$ events collected at the center-of-mass energy $\sqrt{s}$ = 3.0969 GeV with the BESIII detector, we search for the charmonium rare weak decay $J/\psi\to\bar{D}^0\bar{K}^{*0}+{\rm c.c.}$. No significant signal is observed, and the upper limit on its decay branching fraction at the 90% confidence level is set as $1.4\times10^{-7}$, improving the sensitivity of the previous best limit by an order of magnitude.

hep-ex↗