arXiv subjects

W. Chen

Publications and source records attributed to W. Chen.

At least 55 records · Page 3Linked to original sources

arXiv2026

First measurements of the branching fractions of $J/ψ$ and $ψ(3686) \to Σ^{0} \barΣ^{0}η$

Based on $(10087 \pm 44) \times 10^6$ $J/ψ$ and $(2712 \pm 14) \times 10^6$ $ψ(3686)$ events collected with the BESIII detector at the BEPCII collider, the hadronic decays $J/ψ\to Σ^{0} \barΣ^{0} η$ and $ψ(3686) \to Σ^{0} \barΣ^{0} η$ are observed for the first time. The corresponding branching fractions are measured to be $\mathcal{B}(J/ψ\to Σ^{0} \barΣ^{0}η)= (7.5 \pm 0.3 \pm 0.8) \times 10^{-5}$ and $\mathcal{B}(ψ(3686) \to Σ^{0} \barΣ^{0}η)= (1.3\pm 0.1 \pm 0.1) \times 10^{-5}$, respectively, where the first uncertainties are statistical, and the second systematic. The ratio $\text{Q} \approx \frac{\mathcal{B}(ψ(3686) \to Σ^{0} \barΣ^{0} η)}{\mathcal{B}(J/ψ\to Σ^{0} \barΣ^{0} η)}$ is determined to be $(17.3 \pm 1.5 \pm 1.7)\%$, which is con sistent with the 12\%-rule within 3.0$σ$.~No significant intermediate states or threshold enhancements are observed in the $Σ^0$($\barΣ^{0}$)$η$ and $Σ^0$$\barΣ^{0}$ invariant mass spectra.

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arXiv2026

High-precision measurement of the space-like $η^\prime$ transition form factor

Using a data sample corresponding to an integrated luminosity of $20.3\ \text{fb}^{-1}$, collected with the BESIII detector at a center-of-mass energy of $3.773\ \text{GeV}$ at the BEPCII collider, we report a precision measurement of the product $Q^2|F(Q^2)|$, where $F(Q^2)$ is the single-virtual space-like transition form factor of the $η'$ meson and $Q^2$ is the squared momentum transfer of the tagged virtual photon. The transition form factor is extracted from the differential Born cross section of the two-photon fusion processes $e^+e^- \to e^+e^-γγ^* \to e^+e^-η^\prime$ using a single-tag technique, where only one scattered lepton is detected. The measurement covers $Q^2 \in [0.1, 6.0]$ GeV$^2$, achieving unprecedented precision, better than $3.0\%$ for $Q^2 < 1.5$ GeV$^2$, and providing the first direct determination at $Q^2 < 0.3$ GeV$^2$.

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arXiv2026

Observation of $Λ^+_c\to nπ^+η$ and search for $Λ^+_c\to na_0(980)^+$

By analysing 6.1 ${\rm fb}^{-1}$ of data collected at center-of-mass energies between $\sqrt{s}=4.600$ and 4.843 $\rm GeV$ with the BESIII detector at the BEPCII collider, we observe the decay $Λ_c^+\to nπ^+η$ for the first time with a statistical significance of $9.5σ$. The ratio of branching fractions $\mathcal{B}(Λ_c^+\to nπ^+η)/\mathcal{B}(Λ_c^+\to Λπ^+η)$ is measured to be $0.155\pm0.031_{\rm stat.}\pm0.012_{\rm syst.}$ Taking the world average of $\mathcal{B}(Λ_c^+\to Λπ^+η)$ as reference, the absolute branching fraction is calculated to be $\mathcal{B}(Λ_c^+\to nπ^+η)=(2.94\pm0.59_{\rm stat.}\pm0.23_{\rm syst.}\pm0.13_{\rm ref.})\times10^{-3}$. The intermediate process $Λ_c^+\to na_0(980)^+$ is also searched for in the $π^+η$ invariant mass spectrum. Since no significant signal is found, the upper limit on $\mathcal{B}(Λ_c^+\to na_0(980)^+)\times\mathcal{B}(a_0(980)^+\toπ^+η)$ is set to $8.4\times10^{-4}$ at 90\% confidence level. A sophisticated deep learning approach using a Transformer-based architecture is employed to distinguish signals from prevalent hadronic backgrounds, complemented by thorough validation and systematic uncertainty quantification.

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arXiv2026

Search for the charged lepton flavour violating decay $η'\to eμ$

Based on $(8998\pm40)\times10^6$ $J/ψ$ events collected in $e^+e^-$ collisions at $\sqrt{s} = 3.097$ GeV with the BESIII detector, we present a search for the charged lepton flavour violating decay $η'\to eμ$ with $J/ψ\toγη'$. No significant signal is observed, and an upper limit on its decay branching fraction is set to be $6.3\times10^{-7}$ at the 90% confidence level, improving the previous best result by nearly three orders of magnitude.

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arXiv2026

First energy scan measurement of $e^{+}e^{-}\to K^{+}K^{-}$ around the $ψ(2S)$ resonance

We report the precise energy scan measurement of the cross section lineshape of $ψ(2S)\to K^{+}K^{-}$. The analysis is based on $e^{+}e^{-}$ collision data corresponding to an integrated luminosity of 495~pb$^{-1}$ collected with the BESIII detector at BEPCII. By analyzing the cross section line-shape, we extract the relative phase $Φ$ between the strong and electromagnetic amplitudes of the $ψ(2S)$ resonance, a fundamental parameter in charmonium physics, based on the assumption that the relative phase between the electromagnetic amplitude of the $ψ(2S)$ resonance and the continuum is zero. Two distinct solutions for the branching fraction $\mathcal{B}$ of $ψ(2S)\to K^{+}K^{-}$ are observed: a constructive interference solution with $\mathcal{B}=(7.49\pm0.41)\times10^{-5}$ and $Φ=(110.1 \pm6.7)^\circ$, and a destructive interference solution with $\mathcal{B}=(10.94\pm0.48)\times10^{-5}$ and $Φ=(-106.8\pm5.7)^\circ$. A significant correlation between $Φ$ and $\mathcal{B}$ is established, demonstrating that interference effects must be taken into account in the $ψ(2S)$ branching fraction measurements. Additionally, the first results for both the $ψ(2S)$ strong form factor, which characterizes the strong coupling between $ψ(2S)$ and $K^{+}K^{-}$, and the energy-dependent electromagnetic form factor of the charged kaon in this energy region are reported.

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arXiv2026

Precision measurements of semleptonic decays $D^0 \to π^-\ell^+ν_\ell$ and $D^+ \to π^0\ell^+ν_\ell$ ($\ell =e,μ$)

The branching fractions of $D^0\to π^-e^+ν_e$, $D^0\to π^-μ^+ν_μ$, $D^+\to π^0e^+ν_e$, and $D^+\to π^0μ^+ν_μ$ are measured to be $(2.950\pm0.017_{\rm stat.}\pm 0.017_{\rm syst.})\times10^{-3}$, $(2.817\pm0.037_{\rm stat.}\pm 0.019_{\rm syst.})\times10^{-3}$, $(3.622\pm0.034_{\rm stat.}\pm 0.018_{\rm syst.})\times10^{-3}$, and $(3.507\pm0.043_{\rm stat.}\pm 0.026_{\rm syst.})\times10^{-3}$ using $e^+e^-$ collision data with an integrated luminosity of 20.3 fb$^{-1}$ collected at the center-of-mass energy of 3.773 GeV with the BESIII detector. The partial decay rates of these four decays are measured with the best precision to date and their forward-backward asymmetries are determined for the first time. By performing a simultaneous fit to these results, the product of the hadronic transition form factor $f^{D\toπ}_+(0)$ and the modulus of the $c\to d$ Cabibbo-Kobayashi-Maskawa matrix element $|V_{cd}|$ is given by $f^{D\toπ}_+(0)|V_{cd}|=0.1425\pm0.0005_{\rm stat.}\pm0.0003_{\rm syst.}$. Taking the $|V_{cd}|$ provided by the standard model global fit and the $f^{D\toπ}_+(0)$ calculated from the lattice quantum chromodynamics as input, we obtain $f^{D\toπ}_+(0)=0.6339\pm0.0024_{\rm stat.}\pm0.0014_{\rm syst.}$ and $|V_{cd}|=0.2262\pm0.0008_{\rm stat.}\pm0.0005_{\rm syst.}\pm0.0018_{\rm LQCD.}$, respectively. The reported results have the best precision to date. We also search for the scalar current contribution in the $c\to d \ell^+ν_{\ell}$ transition and determine Re$(C_S^μ)=$ $0.022 \pm 0.023_{\rm stat.}\pm 0.003_{\rm syst.}$ and $|{\rm Im}(C_S^μ)|=0.000 \pm $ $0.038_{\rm stat.} \pm 0.012_{\rm syst.}$. In addition, the lepton flavor universality is tested with the ratios of the decay rates between semimuonic and semielectronic decays in full and several $\ell^+ν_\ell$ four-momentum transfer ranges.

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arXiv2026

Precision Measurement of Decay Dynamics in $D^{0(+)}\to π^{-(0)}\ell^+ν_\ell$

The branching fractions of $D^0\to π^-e^+ν_e$, $D^0\to π^-μ^+ν_μ$, $D^+\to π^0e^+ν_e$, and $D^+\to π^0μ^+ν_μ$ are precisely measured, using 20.3 fb$^{-1}$ of $e^+e^-$ collision data collected at the center-of-mass energy of 3.773 GeV with the BESIII detector. The ratios of the decay widths between muon and positron channels are examined in full, across several four-momentum transfer ranges of $\ell^+ν_{\ell}$. No lepton flavor universality violation is found in the current data. From a simultaneous fit to the precisely measured partial decay rates and the first measured forward-backward asymmetries of these four decays, the product of the hadronic transition form factor, $f^{D\toπ}_+(0)$, and the modulus of the $c\to d$ quark mixing element, $|V_{cd}|$, is measured with unprecedented precision to be $f^{D\toπ}_+(0)|V_{cd}|=0.1425\pm0.0005_{\rm stat.}\pm0.0003_{\rm syst.}$. Taking the value of $|V_{cd}|$ from the standard model global fit and $f^{D\toπ}_+(0)$ derived by the lattice quantum chromodynamics calculation as input, we obtain $f^{D\toπ}_+(0)=0.1425\pm0.0005_{\rm stat.}\pm0.0003_{\rm syst.}$ and $|V_{cd}|=0.2262\pm0.0008_{\rm stat.}\pm0.0005_{\rm syst.}\pm0.0018_{\rm LQCD.}$, respectively. The precision of each result is a factor of 2-3 better than the previous best measurements. Additionally, the real and imaginary parts of the scalar current contribution in the $c\to d \ell^+ν_{\ell}$ transition are measured for the first time to be Re $(C_S^μ)=$ $0.022 \pm 0.023_{\rm stat.}\pm 0.003_{\rm syst.}$ and $|\mathrm{Im} (C_S^μ)|=0.000 \pm 0.038_{\rm stat.}\pm 0.012_{\rm syst.}$.

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arXiv2026

Proof of principle for nucleon polarization measurement at BESIII

A novel technique for measuring the spin polarization of final-state nucleons in a general-purpose spectrometer is validated. Using $10.09\times10^{9}$ $J/ψ$ events at BESIII, the asymmetry of polarized proton scattering on detector support material is measured, and is consistent with the expected value. This proves that a general-purpose spectrometer can be utilized as a large-acceptance polarimeter, providing the spin polarization in addition to the conventional four-momentum information of the final-state particles. With this technique, physics capabilities are enhanced for existing and future facilities in particle and nuclear physics.

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arXiv2026

First Measurement of the Relative Phase between Proton Psionic Form Factors

The relative phase between the time-like form factors of the proton is a crucial observable for a complete understanding of its internal structure, yet it has remained unmeasured due to the formidable experimental challenge of determining the final-state polarization or having available polarized beams. With a novel technique that measures polarization via secondary scattering on spectrometer material, we use $10.09\times10^{9}$ $J/ψ$ events collected at BESIII to analyze the reaction $e^+e^-\rightarrow J/ψ\rightarrow p\bar{p}$. This allows the first determination of the sine of the relative phase between the proton psionic form factors, $\sinΔΦ=-0.20\pm0.34_{\textrm{stat}}\pm0.11_{\textrm{syst}}$. This result provides the first direct insight into the complex dynamics of proton formation, and offers valuable new information to constrain theoretical models of nucleon structure.

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arXiv2026

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

Using a data sample of $(1.0087 \pm 0.0044) \times {10^{10}}$ $J/ψ$ events collected with the BESIII detector, we study the rare double Dalitz decay of $η\rightarrow e^+e^-e^+e^-$ through the processes $J/ψ\rightarrow γη$ and $J/ψ\rightarrow γη' ,η' \to π^+π^-η$. Clear $η$ signals are observed in the $e^+e^-e^+e^-$ invariant mass spectrum, with statistical significances of 5.9$σ$ and 7.8$σ$ for the two channels, respectively. By combining both modes, we determine the branching fraction of $η\rightarrow e^+ e^- e^+ e^-$ 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.

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arXiv2026

Observation of $η_{c} \to p\bar{p}η$ via $ψ(3686) \to γp\bar{p}η$

The decay $η_c\to p\bar{p}η$ is observed for the first time with a significance of exceeding $10σ$. It is found by analyzing $(2712.4 \pm 14.3)\times10^{6}$ $ψ(3686)$ events accumulated at the BESIII detector. The measured branching fraction of $η_c\to p\bar{p}η$ via $ψ(3686) \to γp \bar{p} η$ is significantly influenced by the interference between the resonant $η_c$ decay and the non-resonant process $ψ(3686) \to γp \bar{p} η$ and is measured in both constructive- and destructive-interference scenarios. The joint branching fraction of $ψ(3686)\to γη_c$, $η_c\to p\bar{p}η$ is measured to be $(3.2 \pm 0.1 \pm 0.9)\times10^{-6}$ or $(8.7 \pm 0.3 \pm 2.1)\times10^{-6}$ for constructive- or destructive-interference solutions, respectively, where the first uncertainties are statistical and the second systematic. The branching fraction of $η_c\to p\bar{p}η$ is determined to be $\mathcal{B}(η_c\to p\bar{p}η)=(0.90 \pm 0.04 \pm 0.21 \pm 0.13)\times10^{-3}$ or $(2.42 \pm 0.07 \pm 0.48 \pm 0.34)\times10^{-3}$ for the two solutions, respectively, where the third uncertainties are due to the uncertainty in the branching fraction of $ψ(3686)\to γη_c$.

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arXiv2026

Search for an isoscalar partner of the $Z_c(3900)$ in $e^+e^-\toπ^+π^-ηJ/ψ$

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 $e^+e^-\toπ^+π^-ηJ/ψ$ with a statistical significance of $6.0 σ$, including systematic uncertainties. The isoscalar partner of the $Z_c(3900)$, denoted $X(3900)$, is searched for in the $ηJ/ψ$ final state, and no significant signal is observed. The upper limits on the product of the Born cross section $σ^{\rm Born}[e^{+}e^{-}\toπ^{+}π^{-} X(3900)$] and the branching fraction $\mathcal{B}[X(3900)\toηJ/ψ]$ are given with various assumptions for the mass and width of the $X(3900)$.

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arXiv2026

Observation and branching fraction measurements of $J/ψ\to p \bar p K^0_S K^0_S$ and $ψ(3686) \to p \bar p K^0_S K^0_S$

Using $(10.087\pm0.044)\times10^9$ $J/ψ$ events and $(2.712\pm0.014)\times10^9$ $ψ(3686)$ events collected by the BESIII detector operating at the BEPCII collider, we report the first observation of the hadronic decays of $J/ψ\to p \bar p K^0_S K^0_S$ and $ψ(3686) \to p \bar p K^0_S K^0_S$, both with statistical significance greater than $10σ$. Their branching fractions are determined to be $\mathcal{B}(J/ψ\to p \bar p K^0_S K^0_S)=(1.60 \pm 0.02 \pm 0.09)\times10^{-5}$ and $\mathcal{B}(ψ(3686) \to p \bar p K^0_S K^0_S)=(3.93 \pm 0.24 \pm 0.34)\times10^{-6}$. The ratio of their branching fractions is $\mathcal{B}(ψ(3686) \to p \bar p K^0_S K^0_S)/\mathcal{B}(J/ψ\to p \bar p K^0_S K^0_S)=(24.6 \pm 1.5 \pm 2.1)\%$, which deviates from theoretical expectation by 4.6$σ$. Here the first uncertainties are statistical and the second systematic. We have also examined the $p\bar p$ invariant mass distributions in these decays, and no significant enhancement around the $p \bar p$ near threshold is found.

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arXiv2026

Observation of $Ξ(1530)^0$ Polarization and Determination of Its Electric and Magnetic Moments in $ψ(3686)\toΞ(1530)^0\barΞ(1530)^0$

Using the data sample of $2.7\times10^9$ $ψ(3686)$ events collected with the BESIII detector at the BEPCII collider, we present an observation of the $Ξ(1530)^0$ polarization in the decay $ψ(3686)\toΞ(1530)^0\barΞ(1530)^0$ with a significance larger than $20σ$ compared with all other tested hypotheses. The helicity amplitudes for the process $ψ(3686)\toΞ(1530)^0\barΞ(1530)^0$ and the moduli of form factors including electric charge, magnetic dipole, electric quadrupole, and magnetic octupole are measured for the first time by performing an angular distribution analysis. Additionally, the polarization correlations between $Ξ(1530)^0$ and $\barΞ(1530)^0$ are measured.

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arXiv2026

Study of the $e^+e^-\to π^+π^-D_s^+D_s^-$ process from $\sqrt{s}$ = 4.42 to 4.95 GeV at BESIII

Based on $8.5~{\rm fb}^{-1}$ of $e^+e^-$ collision data collected at center-of-mass energies between 4.42 and 4.95 GeV with the BESIII detector at the BEPCII storage ring, we investigate the process $e^+e^-\to π^+π^-D_s^+D_s^-$. With no significant signal observed, upper limits on the Born cross sections of $e^+e^-\to π^+π^-D_s^+D_s^-$ at each energy value are determined at the 90% confidence level. Additionally, a search for intermediate charmonium-like resonances is performed in the $M(D_s^+D_s^-)$ invariant-mass spectrum, but no significant resonant structures are observed with the current statistics.

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arXiv2026

Inclusive jet cross section in $pp$ collisions at $\sqrt{s} = 200$ and $510$ GeV

Jets are collimated clusters of particles formed by the hadronization of partons following a hard interaction. In proton-proton ($pp$) collisions at the Relativistic Heavy Ion Collider (RHIC), jet production is dominated by $gg$ and $qg$ partonic processes, allowing us to directly probe the gluon parton distribution function (PDF) in the proton in a way complementary to deep inelastic scattering. In this paper, we report the double-differential inclusive-jet cross sections as a function of jet transverse momentum, $p_{\rm T}$, and pseudorapidity, $η$, at center-of-mass energies $\sqrt{s} = 200$ and $510$~GeV, from $pp$ collisions studied with the STAR detector. The jet $p_{\rm T}$ is corrected for underlying event contributions by applying an off-axis cone method. At mid-pseudorapidity, $|η| < 0.9$, the kinematic coverage of our data extends to $0.07 < x_{\rm T} \text{ (}= 2p_{\rm T}{} / \sqrt{s} \text{)} < 0.5$ and $0.03 < x_{\rm T} < 0.31$ at $\sqrt{s} = 200$~and 510 GeV, respectively, where the gluon PDF is poorly constrained by the TeV-scale $pp$~($p\bar{p}$) colliders. The inclusive jet cross sections are compared to the next-to-next-to-leading order perturbative quantum chromodynamics calculations using several recent PDF sets as inputs. These results will further constrain the gluon PDF, help tune Monte Carlo generators, and provide critical reference data needed to study the quark-gluon plasma.

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arXiv2026

Observation of $ψ(3770)\to p\bar p$ and Measurement of Electromagnetic Form Factors of Proton at $\sqrt{s} = 3.510-4.946$ GeV

We search for possible charmonium(-like) states decaying into the $p\bar{p}$ final state by studying the Born cross sections of the $e^+e^-\to p\bar{p}$ reaction, and we determine the proton electromagnetic form factors by analyzing the proton angular distribution. The measurement is performed using a sample of $e^+e^-$ collision data collected at 47 center-of-mass energies from 3.510 to 4.946 GeV, corresponding to an integrated luminosity of 26 fb$^{-1}$, recorded by the BESIII detector collected at the BEPCII collider. The decay $ψ(3770)\to p\bar{p}$ is observed with a significance of 6.6$σ$ including systematic uncertainties. Furthermore, a structure near 4.2 GeV is observed with significances of $4.6σ$ or $4.8σ$ for the $ψ(4160)$ or $Y(4230)$ hypotheses including systematic uncertainties, respectively; these interpretations cannot presently be distinguished. In addition, the moduli of the form factor ratios $|G_{E}/G_{M}|$ and of the magnetic form factors $|G_{M}|$ are extracted by analyzing the proton polar angle distribution with higher precision at large time-like squared momentum transfer. These results provide important experimental insights into both the decay mechanisms of charmonium(-like) states in the open charm region and the internal structure of proton.

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arXiv2026

Measurement of Born cross sections for $e^+e^-\to p\bar p$ at $\sqrt{s} =3.510-4.946$ GeV

We report a measurement of the Born cross section and the effective form factor for the $e^+e^-\to p\bar{p}$ reaction at 47 center-of-mass energies between 3.510 and 4.946 GeV. The measurement is performed using the energy-scan technique and is based on data corresponding to an integrated luminosity of 26 fb$^{-1}$ collected with the BESIII detector at the BEPCII collider. For the first time, the moduli of the electromagnetic form factor ratio $|G_{E}/G_{M}|$ and of the magnetic form factor $|G_{M}|$ are determined with high precision by analyzing the distribution of the polar angle of the proton at a large timelike momentum transfer. These results provide essential insights into the nature of charmonium(-like) states above the open-charm threshold and the dynamics underlying the proton electromagnetic form factors.

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