arXiv subjects

Y. T. Feng

Publications and source records attributed to Y. T. Feng.

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.

hep-ex↗

arXiv2026

Search for an isoscalar partner of the $Z_c(3900)$ in $e^+e^-\to\pi^+\pi^-\eta J/\psi$

Using a data sample corresponding to an integrated luminosity of 20.3 fb$^{-1}$ collected at center-of-mass energies from 4.18 to 4.95 GeV with the BESIII detector, we observe the process $e^+e^-\to\pi^+\pi^-\eta J/\psi$ with a statistical significance of $6.0 \sigma$, including systematic uncertainties. The isoscalar partner of the $Z_c(3900)$, denoted $X(3900)$, is searched for in the $\eta J/\psi$ final state, and no significant signal is observed. The upper limits on the product of the Born cross section $\sigma^{\rm Born}[e^{+}e^{-}\to\pi^{+}\pi^{-} X(3900)$] and the branching fraction $\mathcal{B}[X(3900)\to\eta J/\psi]$ are given with various assumptions for the mass and width of the $X(3900)$.

hep-ex↗

arXiv2026

Observation of an Altered $a_{0}(980)$ Line shape in $D^{+} \rightarrow π^{+}ηη$

Using $20.3~{\rm fb}^{-1}$ of $e^+e^-$ collision data collected with the BESIII detector at $\sqrt{s}=3.773~{\rm GeV}$, we perform the first amplitude analysis of the decay $D^+\toπ^+ηη$. The intermediate process $D^+\to a_0(980)^+η$, $a_0(980)^+\toπ^+η$, is observed as the only significant component in the amplitude analysis, and its branching fraction is measured to be $(3.67\pm0.12_{\rm stat}\pm0.06_{\rm syst})\times10^{-3}$. The $π^+η$ mass spectrum associated with $a_0(980)^+η$ production exhibits a line shape that differs substantially from those observed in $D_{(s)}\to a_0(980)π$ and $D^0\to a_0(980)^-e^+ν_e$ decays. We examine several conventional descriptions of the $a_0(980)$ amplitude, including Flatté, dispersively modified Flatté, $T$-matrix, and $K$-matrix parameterizations. With reference $a_0(980)$ parameters, neither these models nor their extensions including additional small resonant or non-resonant amplitudes reproduce the observed line shape satisfactorily. When the $a_0(980)$ parameters are allowed to float, satisfactory fits can be obtained, but the pole mass is driven well above the $K\bar K$ threshold, inconsistent with the near-threshold character of the $a_0(980)$. The results reveal a tension between fit quality and the physical pole position in conventional direct-production amplitude models.

hep-ex↗

arXiv2026

Study of the Magnetic Dipole Transition of $J/ψ\toγη_c$ via $η_c\to p\bar{p}$

Using $(10.087\pm0.044)\times10^9$ $J/ψ$ events collected with the BESIII detector at the $e^+e^-$ BEPCII collider, we present the first amplitude analysis of $J/ψ\toγp\bar{p}$ with the $p\bar p$ invariant mass in the $η_c$ mass region $[2.70,3.05]$~GeV/$c^2$. The product branching fraction $\mathcal{B}(J/ψ\toγη_c)\times\mathcal{B}(η_c\to p\bar{p})$ is precisely determined to be $(2.11\pm0.02_{\rm stat}\pm0.07_{\rm syst})\times10^{-5}$. Combining with the product branching fractions $\mathcal{B}(η_c\to p\bar{p})\times\mathcal{B}(η_c\to γγ)$ and $\mathcal{B}(J/ψ\toγη_c)\times\mathcal{B}(η_c\to γγ)$, the branching fractions of $\mathcal{B}(J/ψ\toγη_c)$ and $\mathcal{B}(η_c\toγγ)$ are calculated to be $(2.29\pm0.01_{\rm stat}\pm0.04_{\rm syst}\pm0.18_{\rm opbf})\%$ and $(2.28\pm0.01_{\rm stat}\pm0.04_{\rm syst}\pm0.18_{\rm opbf})\times10^{-4}$, respectively, which are consistent with the latest lattice quantum chromodynamics calculations. Here, opbf is the uncertainty from the other product branching fractions used in the calculation.

hep-ex↗

arXiv2026

Precise Measurement of Chromoelectric Dipole Moment of the Charm Quark

The combined symmetry of charge conjugation and parity ($C\!P$) is tested in the hadronic transition $ψ(3686)\toπ^+π^{-}J/ψ$, using a dataset of $(2712.4\pm14.3)\times10^6$ $ψ(3686)$ events collected by the BESIII detector at the BEPCII collider. The resulting asymmetry observable is $A_{cp} = (0.6\pm1.8\pm0.1)\times10^{-4}$, which is determined by combining the two channels $J/ψ\to e^+e^-$ and $J/ψ\toμ^+μ^-$. Additionally, by considering the relationship between the chromoelectric dipole moment (CEDM) and the $A_{cp}$ observable derived from the quantum chromodynamics multipole expansion theory based on the Chen-Kuang model and the Cornell potential model, we obtain the results of charm quark's CEDM with $d^{\prime}_{c} = (2.6\pm7.8\pm0.4\pm0.6)\times10^{-16}$ $e$cm, and $d^{\prime}_{c} = (3.5\pm10.5\pm0.6\pm0.5)\times10^{-16}$ $e$cm, respectively. The uncertainties are statistical, systematic, and theoretical, respectively. These results correspond to an upper limit of $|d^{\prime}_{c}|<2.1\times10^{-15}$ $e$ cm at 90\% confidence level, representing an order of magnitude improvement in sensitivity compared to the previous direct bound using the same decay process.

hep-ex↗

arXiv2026

Measurement of the branching fraction of $D_{s}^{*+}\to e^{+}e^{-}D_{s}^{+}$

The branching fraction of the electromagnetic Dalitz decay $D^{*+}_{s}\to e^{+}e^{-}D^{+}_{s}$ is measured with an $e^{+}e^{-}$ collision data sample collected by the BESIII experiment at center-of-mass energies between 4.128 and 4.226 $\mathrm{GeV}$, corresponding to a total integrated luminosity of 7.33 $\mathrm{fb}^{-1}$. The measurement yields the branching fraction ${\mathcal{B}(D^{*+}_{s}\to e^{+}e^{-}D^{+}_{s})=(7.28\pm0.61_{\mathrm{stat}}\pm0.31_{\mathrm{syst}})\times10^{-3}}$. The result is consistent with the previous one, with a 2.5-fold improvement in precision. This provides an important input for constraining the parameters of theoretical models and for determining the absolute branching fractions of $D^{*+}_{s}\to π^{0}D^{+}_{s}$ and $D^{*+}_{s}\to γD^{+}_{s}$, measured with a relative method.

hep-ex↗

arXiv2026

Precision Measurement of $D_{s}^{*+}$-$D_{s}^{+}$ Mass Difference

We measure the mass difference between $D_{s}^{*+}$ and $D_{s}^{+}$, $Δm_s$, using the decay chain $D_{s}^{*+} \to D_{s}^{+}(\to K^{+} K^{-} π^{+})π^{0}$, utilizing $e^+e^-$ annihilation data corresponding to an integrated luminosity of 3.19 fb$^{-1}$ collected at a center-of-mass energy of 4.178 GeV with the BESIII detector. The measured value of $Δm_s = [144\,201.9 \pm 44.2({\rm stat.}) \pm 29.9({\rm syst.}) \pm 15.0({\rm PDG})]$ keV/$c^2$ is about seven times more precise than the current Particle Data Group average, where the last uncertainty is from the Particle Data Group average of the $D^{*+} - D^{+}$ mass difference.

hep-ex↗

arXiv2026

Study of the reactions $\bar{n} p \to 2π^{+}π^{-}$, $2π^{+}π^{-}π^{0}$, and $2π^{+}π^{-}2π^{0}$ using $J/ψ\to p π^{-}\bar{n}$

We report an experimental investigation of the reactions $\bar{n} p \to 2π^{+}π^{-}$, $\bar{n} p \to 2π^{+}π^{-}π^{0}$, and $\bar{n} p \to 2π^{+}π^{-}2π^{0}$ using $(10.087 \pm 0.044) \times 10^{9}$ $J/ψ$ events collected with the BESIII detector at the BEPCII storage ring. The antineutron ($\bar{n}$) is produced in the decay $J/ψ\to p π^{-} \bar{n}$ with studied momentum from 200~MeV/$c$ to 1174~MeV/$c$, while the target proton originates from the hydrogen nuclei in the cooling oil of the beam pipe. This novel method pioneers the study of $\bar{n}$-nucleon interactions at an $e^{+}e^{-}$ collider, providing the first experimental data for $\bar{n}$ momenta exceeding 800~MeV/$c$.

hep-ex↗

arXiv2026

Precise Measurement of Matter-Antimatter Asymmetry with Entangled Hyperon Antihyperon Pairs

A search for $CP$ violation with an entangled system of $Ξ^-\barΞ^+$ pairs is performed, using $(10,087\pm44)\times10^{6}$ $J/ψ$ events collected with the BESIII experiment. A nine-dimensional helicity amplitude is used to fit $e^+e^- \to J/ψ\toΞ^-\barΞ^+$ and its subsequent decays. The $Ξ^-$ and $Ξ^+$ decay parameters are determined with higher precision compared to the best results reported so far. Furthermore, the strong phase difference, $(δ_P-δ_S)=(0.3\pm1.2\pm0.2)\times10^{-2}~\text{rad}$, and the weak phase difference, $(ξ_P-ξ_S)=(-0.2\pm1.2\pm0.1)\times10^{-2}~\text{rad}$, are directly determined. These are the most precise measurements to date. The $CP$ asymmetry observables $A_{CP}^Ξ=(-7.8\pm4.8\pm0.8)\times10^{-3}$ and $Δϕ_{CP}^Ξ=(0.6\pm5.1\pm0.2)\times10^{-3}~\text{rad}$ are determined, which are consistent with $CP$ conservation. In addition, independent measurements of the $Λ$ decay parameter and $CP$ asymmetry $A^Λ_{CP}=(-2.9\pm4.3\pm0.7)\times10^{-3}$ are also obtained, which are in agreement with the previous measurements, but with much improved precision.

hep-ex↗

arXiv2026

Search for the charmonium semi-leptonic weak decay $J/ψ\rightarrow D_s^-e^+ν_e+c.c.$

Using a data sample of $(10087 \pm 44) \times 10^6$ $J/ψ$ events collected with the BESIII detector at a centre-of-mass energy of $\sqrt{s}=3.097\ \textrm{GeV}$, a dedicated search for the charmonium semileptonic weak decay $J/ψ\rightarrow D_s^-e^+ν_e + \text{c.c.}$ is performed. No significant signal is observed. An upper limit on the branching fraction is set at $\mathcal{B}(J/ψ\rightarrow D_s^- e^+ ν_e + \text{c.c.}) < 9.9 \times 10^{-8}$ at the 90\% confidence level. This result improves upon previous constraints by an order of magnitude, representing the most stringent experimental limit to date. It thus provides a critical test of Standard Model predictions and new physics scenarios in heavy-quark dynamics.

hep-ex↗

arXiv2026

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

Based on a sample of $(10087\pm44)\times10^6$ $J/ψ$ 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 $J/ψ\to\bar{D}^0\bar{K}^{*0}+{\rm c.c.}$. 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↗

arXiv2026

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

We present the first amplitude analysis of the hadronic decay $D^+\toπ^+π^0π^0$, 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 $D^+ \to ρ(770)^+π^0$ 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 $D^+ \to π^+π^0π^0$ 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.

hep-ex↗

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.

hep-ex↗

arXiv2026

Measurement of the double Dalitz decay $\eta \to e^+e^-e^+e^-$

Using a data sample of $(1.0087 \pm 0.0044) \times {10^{10}}$ $J/{\psi}$ events collected with the BESIII detector, we study the rare double Dalitz decay of $\eta\rightarrow e^+e^-e^+e^-$ through the processes $J/\psi\rightarrow \gamma \eta$ and $J/\psi\rightarrow \gamma \eta' ,\eta' \to \pi^+\pi^-\eta$. Clear $\eta$ signals are observed in the $e^+e^-e^+e^-$ invariant mass spectrum, with statistical significances of 5.9$\sigma$ and 7.8$\sigma$ for the two channels, respectively. By combining both modes, we determine the branching fraction of $\eta\rightarrow e^+ e^- e^+ e^-$ to be $(2.63~\pm~0.34_{\rm stat}~\pm~0.16_{\rm syst}) \times10^{-5}$. The result is consistent with the previous measurements within uncertainties and further constrains physics beyond the standard model.

hep-ex↗

arXiv2026

Evidence of transverse polarization of $Ξ^0$ hyperon in $ψ(3686)\rightarrowΞ^0\barΞ^0$

Using $(2.712\pm0.014)\times10^{9}$ $ψ(3686)$ events collected with the BESIII detector at the BEPCII collider, we report an evidence of $Ξ^{0}$ transverse polarization with a significance of 4.4$σ$, a precise measurement of the branching fraction and the ratios between the $S$-wave and $D$-wave contributions of $ψ(3686)\toΞ^{0}\barΞ^{0}$. The weak decay parameters ($ϕ_{Ξ^0/\barΞ^{0}}$, $α_{Ξ^0/\barΞ^{0}}$) and the angular distribution ($α_ψ$) are also measured with higher precision compared to the previous measurements. Furthermore, two the $CP$ observables are also determined to be $A^{Ξ^0}_{CP} = -0.014 \pm 0.030 \pm 0.010$ and $Δϕ^{Ξ^0}_{CP} = 0.000 \pm 0.028 \pm 0.003$~rad, which are still consistent with $CP$ conservation at 1$σ$ level under the current statistics.

hep-ex↗

arXiv2026

Search for the decays $X(3872)\to K_{S}^{0}K^{\pm}π^{\mp}$ and $K^*(892)\bar{K}$ at BESIII

Using a 10.9 fb$^{-1}$ data sample collected by the BESIII detector at center-of-mass energies from 4.16 to 4.34 GeV, we search for the charmless decays $X(3872) \to K_{S}^{0}K^{\pm}π^{\mp}$ and $K^*(892)\bar{K}$, where the $X(3872)$ is produced via the radiative process $e^+e^- \to γX(3872)$. No significant signal is observed. We set upper limits on the relative branching fractions $\mathcal{B}[X(3872)\to K_S K^{\pm} π^{\mp}]/\mathcal{B}[X(3872)\toπ^+π^- J/ψ] <0.07$ and $\mathcal{B}[X(3872)\to K^* (892)\bar{K}]/\mathcal{B}[X(3872)\to π^+π^- J/ψ] <0.10$ at the 90$\%$ confidence level. Additionally, upper limits on the product of the cross section $σ[e^+e^-\toγX(3872)]$ and the branching fractions $\mathcal{B}[X(3872)\to K_{S}^{0}K^{\pm}π^{\mp}]$ and $\mathcal{B}[X(3872)\to K^*(892)\bar{K}]$ are reported at each energy point. In all cases, $K^*(892)\bar{K}$ refers to the sum of the modes $K^*(892)^+K^{-}+\text{c.c.}$ and $K^*(892)^0\bar{K}^0+\text{c.c.}$, where c.c. denotes the corresponding charge-conjugate modes.

hep-ex↗

arXiv2026

Consistent control of energy dissipation in non-spherical particle contact via a structure-preserving formulation

The control of energy dissipation in non-spherical particle contact remains an unresolved problem. Unlike spherical contact, where the interaction reduces to a one-dimensional normal oscillator, both the effective inertia and the effective stiffness depend on the evolving contact geometry, and the impact dynamics are intrinsically coupled across translational, rotational, and tangential directions. Classical damping formulations are therefore structurally incompatible with the contact dynamics they are intended to represent. This work addresses the problem from first principles. By projecting the dynamics onto contact degrees of freedom, the interaction is shown to be governed by an instantaneous contact dynamics with a configuration-dependent projected mass and intrinsic translational--rotational coupling. Building on the exact energy--phase transformation for monotone conservative contact, we show that consistent dissipation requires a unique damping structure aligned with the underlying contact energy. The analysis leads to two central consequences. First, the admissible damping law is not empirical but fixed by the harmonic structure revealed in transformed space. Second, the appropriate coefficient of restitution for non-spherical particles is the contact-point restitution $e_{cn}$, whereas the total energy restitution $e_E$ is a geometry-dependent outcome that includes coupling-induced energy transfer. Numerical evidence based on smooth single-contact impacts confirms the theory: the resulting formulation controls $e_{cn}$ consistently across impact configurations, while the apparent variability of $e_E$ follows directly from the coupled dynamics.

physics.comp-ph↗

arXiv2026

Observation of a threshold enhancement in the $π^+π^-$ spectrum in $ψ(3686) \rightarrow π^{+}π^{-}J/ψ$ decays

Based on the $(2712.4\pm14.4)\times 10^{6}$ $ψ(3686)$ events collected with the BESIII detector, we present a high-precision study of the $π^+π^-$ mass spectrum in $ψ(3686)\rightarrowπ^{+}π^{-}J/ψ$ decays. A clear resonance like structure is observed near the $π^+π^-$ mass threshold for the first time. A fit with a Breit-Wigner function yields a mass of $285.6\pm 2.5~{\rm MeV}/c^2$ and a width of $16.3\pm 0.9~{\rm MeV}$ with a statistical significance exceeding 10$σ$. To interpret the data, we incorporate final state interactions (FSI) within two theoretical frameworks: chiral perturbation theory (ChPT) and QCD multipole expansion (QCDME). ChPT describes the spectrum above 0.3 GeV/$c^2$ but fails to reproduce the threshold enhancement. In contrast, the QCDME model assuming the $ψ(3686)$ is an admixture of S and D wave charmonium reproduces the data well. The pronounced dip near 0.3 GeV/$c^2$ offers new insight into the interplay between chiral dynamics and low-energy QCD.

hep-ex↗