arXiv subjects

Q. An

Publications and source records attributed to Q. An.

At least 19 recordsLinked to original sources

arXiv2026

Search for the doubly Cabibbo-suppressed decays $D^0\to K^+\pi^-\eta^\prime$ and $D^+\to K^+\pi^0\eta^\prime$

We present the first search for the doubly Cabibbo-suppressed decays $D^0\to K^+\pi^-\eta^\prime$ and $D^+\to K^+\pi^0\eta^\prime$ using an $e^+e^-$ collision data sample corresponding to an integrated luminosity of 20.3 fb$^{-1}$, collected at a center-of-mass energy of 3.773 GeV with the Beijing Spectrometer III (BESIII) detector at the Beijing Electron-Positron Collider II (BEPCII). No significant signals are observed, and the upper limits on their decay branching fractions are set to be $3.0\times 10^{-5}$ and $2.1\times 10^{-5}$ at the 90% confidence level, respectively. By combining these results with the world-average branching fractions of the corresponding Cabibbo-favored decays, upper limits at the 90% confidence level are obtained on the ratios of doubly Cabibbo-suppressed to Cabibbo-favored branching fractions. The limits are determined to be $1.6\times \tan^4\theta_C$ and $3.7\times \tan^4\theta_C$ for $D^0\to K^+\pi^-\eta^\prime$ and $D^+\to K^+\pi^0\eta^\prime$, respectively, where $\theta_C$ denotes the Cabibbo mixing angle.

hep-ex↗

arXiv2026

Measurement of CP Asymmetry Parameters and Polarization Correlations in $\Omega^{-}\bar{\Omega}^{+}$ Pairs

Using $(2.71 \pm 0.01) \times 10^9$ $\psi(3686)$ events collected with the BESIII detector, a joint full angular distribution analysis is carried out for the process $\psi(3686) \to \Omega^-(\to\Lambda K^-) \, \bar{\Omega}^{+}(\to \bar{\Lambda}K^+)$. The first simultaneous measurement of the weak decay parameters $\phi_{\Omega^{-}}$ and $\phi_{\bar{\Omega}^{+}}$ for $\Omega^- \to K^-\Lambda$ and $\bar{\Omega}^+ \to K^+\bar{\Lambda}$ is performed, yielding the first result for the CP-sensitive observable, $\phi_{\rm CP} = (-0.004 \pm 0.055 \pm 0.017)~\text{rad}$, where the first and second uncertainties are statistical and systematic, respectively. This further enables the extraction of the weak and strong phase differences between the $P$- and $D$-wave amplitudes: $(\xi_D - \xi_P) = (-0.15 \pm 2.25 \pm 0.69)~\text{rad}$ and $(\delta_D - \delta_P) = (-0.97 \pm 0.88 \pm 0.34)~\text{rad}$. Additionally, the polarization correlations between $\Omega^{-}$ and $\bar{\Omega}^{+}$ are measured.

hep-ex↗

arXiv2026

Study of $K_{S}^{0}$-$K_{L}^{0}$ asymmetry in the decays $D^0 \to K_{S}^{0}\omega $ and $D^0 \to K_{L}^{0} \omega $

Based on $e^+ e^-$ annihilation data corresponding to an integrated luminosity of 7.93~$fb^{-1}$ collected at a center-of-mass energy of 3.773 GeV with the BESIII detector at the BEPCII collider, the absolute branching fractions of the decays $D^0 \to K_{S}^{0} \omega$ and $D^0 \to K_{L}^{0} \omega $ are measured to be $(11.79 \pm 0.19 \pm 0.26 \pm 0.47) \times 10^{-3}$ and ($10.84 \pm 0.14 \pm 0.23 \pm 0.44) \times 10^{-3}$, respectively. The $K_{S}^{0}- K_{L}^{0}$ branching-fraction asymmetry of these two decays is $R(D^0,K_{S,L}^{0} \omega) = \frac{\mathcal{B}(D^0 \to K_{S}^{0} \omega) - \mathcal{B}(D^0 \to K_{L}^{0}\omega )}{\mathcal{B}(D^0 \to K_{S}^{0} \omega) + \mathcal{B}(D^0 \to K_{L}^{0} \omega)} =(4.2 \pm 1.0 \pm 0.9 \pm 2.8)\%$. Here, the first uncertainties are statistical, the second systematic, and the third arise from the interference between $D^0 \to K_{S,L}^{0} \omega$ and the non-resonant $D^0 \to \pi^+ \pi^- \pi^0 K_{S,L}^{0}$ processes.

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arXiv2026

Search for the baryonic decay $ D_{s}^{*+} \to \ p \bar{n} $

The first search for the baryonic decay $ D_{s}^{*+} \to \ p \bar{n} $ is performed using $e^+e^-$ collision data taken at center-of-mass energies between 4.128 and 4.226 GeV, collected by the BESIII experiment and corresponding to an integrated luminosity of 7.33 fb$^{-1}$. No significant signal is observed, and an upper limit on the branching fraction is set to be $1.3\times 10^{-4}$ at the $90\%$ confidence level.

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arXiv2026

Observation of $\psi(3686)\to p K^- K_S^0 \bar \Xi^0+c.c.$

Using a sample of $(2.712 \pm 0.014) \times 10^{9}$ $\psi(3686)$ events collected with the BESIII detector, the decay of $\psi(3686)\to p K^- K_S^0 \bar \Xi^0+c.c.$ is observed for the first time with a statistical significance of $11.5\sigma$. The branching fraction of this decay is measured to be $(2.84\pm 0.40\pm 0.25) \times 10^{-6}$, where the first and second uncertainties are statistical and systematic, respectively. This measurement extends the experimental information on rare multi-strange $\psi(3686)$ decays and provides an experimental reference for future studies of related decay modes.

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arXiv2026

Measurement of inelastic scattering $\Lambda(\overline{\Lambda})+p\to\Sigma^{0}(\overline{\Sigma}^{0})+p$ via $e^+e^-\to J/\psi\to\Lambda\overline{\Lambda}$

Using a sample of $(10087\pm44)\times10^{6}$ $J/\psi$ events collected with the BESIII detector, we investigate the inelastic scattering processes $\Lambda+p\to\Sigma^{0}+p$ and $\overline{\Lambda}+p\to\overline{\Sigma}^{0}+p$, exploiting hyperons from $J/\psi\to\Lambda\overline{\Lambda}$ decays as an effective beam and the beam-pipe materials as targets. The processes $\Lambda+{}^{9}\mathrm{Be}\to\Sigma^{0}+p+{}^{8}\mathrm{Li}$ and $\overline{\Lambda}+{}^{9}\mathrm{Be}\to\overline{\Sigma}^{0}+p+{}^{8}\mathrm{Li}$ are measured at a hyperon momentum of $1.074~\mathrm{GeV}/c$, with cross sections of $(10.1\pm1.4_{\rm stat}\pm0.7_{\rm syst})$ mb and $(1.7\pm0.6_{\rm stat}\pm0.4_{\rm syst})$ mb, respectively. Under the assumption of surface-dominated hyperon-nucleus scattering, these measurements are used to extract the corresponding proton-target cross sections. Independently, direct measurements using the hydrogen component of the beam-pipe oil yield $(3.2\pm1.1_{\rm stat}\pm0.5_{\rm syst})$ mb for $\Lambda+p\to\Sigma^{0}+p$ and $(1.5\pm0.5_{\rm stat}\pm0.1_{\rm syst})$ mb for $\overline{\Lambda}+p\to\overline{\Sigma}^{0}+p$, consistent with the indirect determinations. The combined cross sections are $(4.7\pm0.7)$ mb and $(1.1\pm0.3)$ mb, respectively. The $\overline{\Lambda}+p\to\overline{\Sigma}^{0}+p$ signal constitutes the first evidence for anti-hyperon inelastic scattering with baryonic final states, with a significance of $3.1\sigma$. The pronounced difference between the $\Lambda p$ and $\overline{\Lambda}p$ inelastic scattering cross sections provides new experimental constraints on hyperon-nucleon and anti-hyperon-nucleon interactions.

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arXiv2026

Evidence for $\eta_{c}(2S)\to p\bar{p}\pi^{+}\pi^{-}\pi^{0}$ and observation of $\chi_{cJ} \to p\bar{p}\pi^{+}\pi^{-}\pi^{0}$

Using $(2.712\pm0.014)\times 10^9$ $\psi(3686)$ events collected by the BESIII detector at the BEPCII collider, the $\psi(3686) \to \gamma p\bar{p}\pi^+\pi^-\pi^0$ process is investigated. Evidence for the decay of $\eta_{c}(2S)\to p\bar{p}\pi^{+}\pi^{-}\pi^{0}$ is found with a signal significance of 3.3$\sigma$. The product of branching fractions of $\mathcal{B}[\psi(3686)\to \gamma \eta_{c}(2S)]\times\mathcal{B}[\eta_{c}(2S)\to p\bar{p}\pi^{+}\pi^{-}\pi^{0}]$ is determined to be $(3.4\pm0.5\pm0.8) \times 10^{-6}$, where the first uncertainty is statistical and the second systematic. The hadronic decays of $\chi_{cJ} \to p\bar{p}\pi^+\pi^-\pi^0$$~(J=0,1,2)$ are observed, and their branching fractions are measured to be $\mathcal{B}(\chi_{c0}\to p\bar{p}\pi^{+}\pi^{-}\pi^{0})=(4.79\pm 0.01\pm0.40) \times 10^{-3}$, $\mathcal{B}(\chi_{c1}\to p\bar{p}\pi^{+}\pi^{-}\pi^{0})=(2.13\pm 0.01\pm0.17) \times 10^{-3}$, and $\mathcal{B}(\chi_{c2}\to p\bar{p}\pi^{+}\pi^{-}\pi^{0})=(3.72\pm 0.01\pm0.29) \times 10^{-3}$, respectively. Furthermore, the branching fractions for the intermediate processes $\chi_{cJ}\to p\bar{p}\omega$ are updated with significantly improved precision: $\mathcal{B}(\chi_{c0}\to p\bar{p}\omega)=(5.76\pm0.01\pm0.42)\times10^{-4}$, $\mathcal{B}(\chi_{c1}\to p\bar{p}\omega)=(1.85\pm0.01\pm0.13)\times10^{-4}$, and $\mathcal{B}(\chi_{c2}\to p\bar{p}\omega)=(4.51\pm0.01\pm0.33)\times10^{-4}$, respectively.

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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

First measurements of the branching fractions of $J/\psi$ and $\psi(3686) \to \Sigma^{0} \bar{\Sigma}^{0}\eta$

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

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arXiv2026

High-precision measurement of the space-like $\eta^\prime$ 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 $\eta'$ 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 $e^+e^- \to e^+e^-\gamma\gamma^* \to e^+e^-\eta^\prime$ 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$^2$.

hep-ex↗

arXiv2026

Search for the charged lepton flavour violating decay $\eta'\to e\mu$

Based on $(8998\pm40)\times10^6$ $J/\psi$ 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 $\eta'\to e\mu$ with $J/\psi\to\gamma\eta'$. 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

Precision measurements of semleptonic decays $D^0 \to \pi^-\ell^+\nu_\ell$ and $D^+ \to \pi^0\ell^+\nu_\ell$ ($\ell =e,\mu$)

The branching fractions of $D^0\to \pi^-e^+\nu_e$, $D^0\to \pi^-\mu^+\nu_\mu$, $D^+\to \pi^0e^+\nu_e$, and $D^+\to \pi^0\mu^+\nu_\mu$ 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 $f^{D\to\pi}_+(0)$ and the modulus of the $c\to d$ Cabibbo-Kobayashi-Maskawa matrix element $|V_{cd}|$ is given by $f^{D\to\pi}_+(0)|V_{cd}|=0.1425\pm0.0005_{\rm stat.}\pm0.0003_{\rm syst.}$. Taking the $|V_{cd}|$ provided by the standard model global fit and the $f^{D\to\pi}_+(0)$ calculated from the lattice quantum chromodynamics as input, we obtain $f^{D\to\pi}_+(0)=0.6339\pm0.0024_{\rm stat.}\pm0.0014_{\rm syst.}$ 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 $c\to d \ell^+\nu_{\ell}$ transition and determine Re$(C_S^\mu)=$ $0.022 \pm 0.023_{\rm stat.}\pm 0.003_{\rm syst.}$ and $|{\rm Im}(C_S^\mu)|=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 $\ell^+\nu_\ell$ four-momentum transfer ranges.

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arXiv2026

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

The branching fractions of $D^0\to \pi^-e^+\nu_e$, $D^0\to \pi^-\mu^+\nu_\mu$, $D^+\to \pi^0e^+\nu_e$, and $D^+\to \pi^0\mu^+\nu_\mu$ 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 $\ell^+\nu_{\ell}$. 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, $f^{D\to\pi}_+(0)$, and the modulus of the $c\to d$ quark mixing element, $|V_{cd}|$, is measured with unprecedented precision to be $f^{D\to\pi}_+(0)|V_{cd}|=0.1425\pm0.0005_{\rm stat.}\pm0.0003_{\rm syst.}$. Taking the value of $|V_{cd}|$ from the standard model global fit and $f^{D\to\pi}_+(0)$ derived by the lattice quantum chromodynamics calculation as input, we obtain $f^{D\to\pi}_+(0)=0.1425\pm0.0005_{\rm stat.}\pm0.0003_{\rm syst.}$ 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 $c\to d \ell^+\nu_{\ell}$ transition are measured for the first time to be Re $(C_S^\mu)=$ $0.022 \pm 0.023_{\rm stat.}\pm 0.003_{\rm syst.}$ and $|\mathrm{Im} (C_S^\mu)|=0.000 \pm 0.038_{\rm stat.}\pm 0.012_{\rm syst.}$.

hep-ex↗

arXiv2026

Measurement of Born Cross Section for $e^+e^-\to K_S^0\bar{\Xi}^+\Sigma^-+\rm{c.c.}$ at $\sqrt{s} = 3.51-4.95$ GeV

Using $e^+e^-$ collision data collected with the BESIII detector at the BEPCII collider corresponding to a total integrated luminosity of 44~fb$^{-1}$, we present the first measurement of the Born cross sections for the process $e^+e^-\to K_S^0\bar{\Xi}^+\Sigma^-+\rm{c.c.}$ at 56 center-of-mass energies from 3.510 to 4.951~GeV. By fitting the dressed cross sections of $e^+e^-\to K_S^0\bar{\Xi}^+\Sigma^-+\rm{c.c.}$ with the assumption of a power-law function plus a charmonium(-like) resonance, i.e. $\psi(3770)$, $\psi(4040)$, $\psi(4160)$, $Y(4230)$, $Y(4360)$, $\psi(4415)$, {\it Y}(4500), $Y(4660)$, and {\it Y}(4710), no significant signal of any charmonium(-like) state decaying into the $K_S^0\bar{\Xi}^+\Sigma^-+\rm{c.c.}$ is observed. Upper limits on the product of the electronic width and branching fraction at the 90\% confidence level are given for each resonance. Combining this result with the previous measurement of the isospin-symmetric process $e^+e^-\to K^{-} \bar{\Xi}^{+} \Sigma^{0} + \rm{c.c.}$, the ratio of the Born cross sections, $R=\sigma^{B}(e^+e^-\to K_S^0\bar{\Xi}^+\Sigma^-+\rm{c.c.})/$$\sigma^{B}(e^+e^-\to K^-\bar{\Xi}^+\Sigma^0+\rm{c.c.})$, is found to be approximately 1.

hep-ex↗

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 $10.09\times10^{9}$ $J/\psi$ 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 $10.09\times10^{9}$ $J/\psi$ events collected at BESIII to analyze the reaction $e^+e^-\rightarrow J/\psi \rightarrow p\bar{p}$. This allows the first determination of the sine of the relative phase between the proton psionic form factors, $\sin\Delta\Phi=-0.20\pm0.34_{\textrm{stat}}\pm0.11_{\textrm{syst}}$. 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.

hep-ex↗

arXiv2026

Observation of $\eta_{c} \to p\bar{p}\eta$ via $\psi(3686) \to \gamma p\bar{p}\eta$

The decay $\eta_c\to p\bar{p}\eta$ is observed for the first time with a significance of exceeding $10\sigma$. It is found by analyzing $(2712.4 \pm 14.3)\times10^{6}$ $\psi(3686)$ events accumulated at the BESIII detector. The measured branching fraction of $\eta_c\to p\bar{p}\eta$ via $\psi(3686) \to \gamma p \bar{p} \eta$ is significantly influenced by the interference between the resonant $\eta_c$ decay and the non-resonant process $\psi(3686) \to \gamma p \bar{p} \eta$ and is measured in both constructive- and destructive-interference scenarios. The joint branching fraction of $\psi(3686)\to \gamma\eta_c$, $\eta_c\to p\bar{p}\eta$ 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 $\eta_c\to p\bar{p}\eta$ is determined to be $\mathcal{B}(\eta_c\to p\bar{p}\eta)=(0.90 \pm 0.04 \pm 0.21 \pm 0.13)\times10^{-3}$ 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 $\psi(3686)\to \gamma \eta_c$.

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↗