arXiv subjects

Y. L. Fan

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

At least 19 recordsLinked to original sources

arXiv2025

Test of local realism via entangled $\Lambda\bar\Lambda$ system

The non-locality of quantum correlations is a fundamental feature of quantum theory. The Bell inequality serves as a benchmark for distinguishing between predictions made by quantum theory and local hidden variable theory (LHVT). Recent advancements in photon-entanglement experiments have addressed potential loopholes and have observed significant violations of variants of Bell inequality. However, examples of Bell inequalities violation in high energy physics are scarce. In this study, we utilize $(10.087\pm0.044)\times10^{9}$ $J/\psi$ events collected with the BES-III detector at the BEPCII collider, performing non-local correlation tests using the entangled hyperon pairs. The massive-entangled $\Lambda\bar\Lambda$ systems are formed and decay through strong and weak interactions, respectively. Through measurements of the angular distribution of $p\bar{p}$ in $J/\psi\to \gamma\eta_c$ and subsequent $\eta_c\to\Lambda(p\pi^-)\bar\Lambda(\bar{p}\pi^{+})$ cascade decays, a significant violation of LHVT predictions is observed. The exclusion of LHVT is found to be statistically significant at a level exceeding $5.2\sigma$ in the testing of three Bell-like inequalities.

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arXiv2024

Measurement of the Inclusive Cross Sections of Prompt $J/\psi$ and $\psi(3686)$ Production in $e^{+}e^{-}$ Annihilation from $\sqrt{s}=3.808$ to $4.951$ GeV

The inclusive cross sections of prompt $J/\psi$ and $\psi(3686)$ production are measured at center-of-mass energies from 3.808 to 4.951 GeV. The dataset used is 22 fb$^{-1}$ of $e^{+}e^{-}$ annihilation data collected with the BESIII detector operating at the BEPCII storage ring. The results obtained are in agreement with the previous BESIII measurements of exclusive $J/\psi$ and $\psi(3686)$ production. The average values obtained for the cross sections measured in the center-of-mass energy ranges from 4.527 to 4.951 GeV for $J/\psi$ and from 4.843 to 4.951 GeV for $\psi(3686)$, where the impact of known resonances is negligible, are $14.0\pm1.7\pm3.1$ pb and $15.3\pm3.0$ pb, respectively. For $J/\psi$, the first and the second uncertainties are statistical and systematic, respectively. For $\psi(3686)$, the uncertainty is total. These values are useful for testing charmonium production models.

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arXiv2024

Observation of the Electromagnetic Dalitz Transition $h_c \rightarrow e^+e^-\eta_c$

Using $(27.12\pm 0.14)\times10^8$ $\psi(3686)$ decays and data samples of $e^+e^-$ collisions with $\sqrt{s}$ from 4.130 to 4.780~GeV collected with the BESIII detector, we report the first observation of the electromagnetic Dalitz transition $h_c\to e^+e^-\eta_c$ with a statistical significance of $5.4\sigma$. We measure the ratio of the branching fractions $\frac{\mathcal{B}(h_c\rightarrow e^+e^-\eta_c)}{\mathcal{B}(h_c\rightarrow \gamma \eta_c)}$ separately for the $h_c$ samples produced via $\psi(3686)\to\pi^0h_c$ and $e^+e^-\to\pi^+\pi^-h_c$. The average ratio is determined to be $(0.59\pm0.10(\text{stat.})\pm0.04(\text{syst.}))\%$, where the uncertainty includes both statistical and systematic components.

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arXiv2024

Evidence of the Singly Cabibbo Suppressed decay $Λ_c^+\to pπ^0$

Evidence for the singly Cabibbo suppressed decay $Λ_c^+\to pπ^0$ is reported for the first time with a statistical significance of $3.7σ$ based on 6.0 $\mathrm{fb}^{-1}$ of $e^+e^-$ collision data collected at center-of-mass energies between 4.600 and 4.843 GeV with the BESIII detector at the BEPCII collider. The absolute branching fraction of $Λ_c^+\to pπ^0$ is measured to be $(1.56^{+0.72}_{-0.58}\pm0.20)\times 10^{-4}$. Combining with the branching fraction of $Λ_c^+\to nπ^+$, $(6.6\pm1.3)\times10^{-4}$, the ratio of the branching fractions of $Λ_c^+\to nπ^+$ and $Λ_c^+\to pπ^0$ is calculated to be $3.2^{+2.2}_{-1.2}$. As an important input for the theoretical models describing the decay mechanisms of charmed baryons, our result indicates that the non-factorizable contributions play an essential role and their interference with the factorizable contributions should not be significant. In addition, the absolute branching fraction of $Λ_c^+\to pη$ is measured to be $(1.63\pm0.31_{\rm stat}\pm0.11_{\rm syst}) \times10^{-3}$.

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arXiv2024

Search for the leptonic decays $D^{+}\to e^+\nu_e$ and $D^{+}\to \mu^+\nu_\mu$

We present the first search for the leptonic decays $D^{*+}\to e^+\nu_e$ and $D^{*+}\to \mu^+\nu_\mu$ by analyzing a data sample of electron-positron collisions recorded with the BESIII detector at center-of-mass energies between 4.178 and 4.226 GeV, corresponding to an integrated luminosity of 6.32~fb$^{-1}$. No significant signal is observed. The upper limits on the branching fractions for $D^{*+}\to e^+\nu_e$ and $D^{*+}\to \mu^+\nu_\mu$ are set to be $1.1 \times 10^{-5}$ and $4.3 \times 10^{-6}$ at 90\% confidence level, respectively.

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arXiv2024

Measurement of the absolute branching fraction of the three-body decay $Λ_{c}^+ \to Ξ^{0}K^{+}π^{0}$ and search for $Λ_{c}^+ \to nK^+π^0$, $Σ^{0}K^{+}π^{0}$ and $ΛK^{+}π^{0}$

The Cabbibo-favored decay $Λ_{c}^+ \to Ξ^{0}K^{+}π^{0}$ is studied for the first time using 6.1 fb$^{-1}$ of $e^+e^-$ collision data at center-of-mass energies between 4.600 and 4.840 GeV, collected with the BESIII detector at the BEPCII collider. With a double-tag method, the branching fraction of the three-body decay $Λ_{c}^+ \to Ξ^{0}K^{+}π^{0}$ is measured to be $(7.79 \pm 1.46 _{\rm} \pm0.71 _{\rm}) \times 10^{ - 3}$, where the first and second uncertainties are statistical and systematic, respectively. The branching fraction of the two-body decay $Λ_{c}^+ \to Ξ(1530)^{0}K^+$ is $(5.99\pm1.04\pm0.29)\times10^{-3}$, which is consistent with the previous result of $(5.02\pm0.99\pm0.31)\times 10^{-3}$. In addition, the upper limit on the branching fraction of the doubly Cabbibo-suppressed decay $Λ_{c}^+ \to nK^+π^0$ is $7.1 \times 10^{-4}$ at the 90$\%$ confidence level. The upper limits on the branching fractions of $Λ_{c}^+ \to Σ^{0}K^{+}π^{0}$ and $ΛK^{+}π^{0}$ are also determined to be $1.8\times 10^{-3}$ and $ 2.0 \times 10^{-3}$, respectively.

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arXiv2024

Observation of the Singly Cabibbo-Suppressed Decay $Λ_{c}^{+}\to Σ^{-}K^{+}π^{+}$

The singly Cabibbo-suppressed decay $Λ_{c}^{+}\to Σ^{-}K^{+}π^{+}$ is observed for the first time with a statistical significance of $6.4σ$ by using 4.5 fb$^{-1}$ of $e^+e^-$ collision data collected at center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at BEPCII. The absolute branching fraction of $Λ_{c}^{+}\to Σ^{-}K^{+}π^{+}$ is measured to be $(3.8\pm1.3_{\rm stat}\pm0.2_{\rm syst})\times 10^{-4}$ in a model-independent approach. This is the first observation of a Cabibbo-suppressed $Λ_{c}^{+}$ decay involving $Σ^-$ in the final state. The ratio of branching fractions between $Λ_{c}^{+}\to Σ^{-}K^{+}π^{+}$ and the Cabibbo-favored decay $Λ_{c}^{+}\to Σ^- π^+π^+$ is calculated to be $(0.4 \pm 0.1)s_{c}^{2}$, where $s_{c} \equiv \sinθ_c = 0.2248$ with $θ_c$ the Cabibbo mixing angle. This ratio significantly deviates from $1.0s_{c}^{2}$ and provides important information for the understanding of nonfactorization contributions in $Λ_{c}^{+}$ decays.

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arXiv2024

Study of excited $Ξ$ states in $ψ(3686)\rightarrow{}K^{-}Λ\overlineΞ^{+}+c.c.$

Based on a sample of $(448.1\pm2.9)\times10^{6}$ $ψ(3686)$ events collected with the BESIII detector at BEPCII, the decays of $ψ(3686)\to{}K^{-}Λ\overlineΞ^{+} + c.c.$ with $\overlineΞ^+ \to \overlineΛ π^+$, $\overlineΛ\to \overline{p} π^+$ are studied.Two excited hyperons, $Ξ(1690)^-$ and $Ξ(1820)^-$, are observed with large significance ($ \gg 10 σ$) in the $K^{-}Λ$ invariant mass distributions. A partial wave analysis is performed, and the spin-parities of $Ξ(1690)^-$ and $Ξ(1820)^-$ are determined to be $\frac{1}{2}^{-}$ and $\frac{3}{2}^{-}$, respectively. The masses, widths, and product branching fractions of $Ξ(1690)^-$ and $Ξ(1820)^-$ are also measured.

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arXiv2024

Observation of the Anomalous Shape of $X(1840)$ in $J/ψ\rightarrow γ3(π^+ π^-)$ Indicating a Second Resonance Near $p\bar{p}$ Threshold

Using a sample of $(10087\pm44)\times 10^6$ $J/ψ$ events, which is about 45 times larger than that was previously analyzed, a further investigation on the $J/ψ\rightarrow γ3(π^+π^-)$ decay is performed. A significant distortion at 1.84 GeV/$c^2$ in the line-shape of the $3(π^+π^-)$ invariant mass spectrum is observed for the first time, which could be resolved by two overlapping resonant structures, $X(1840)$ and $X(1880)$. The new state $X(1880)$ is observed with a statistical significance larger than $10σ$. The mass and width of $X(1880)$ are determined to be $1882.1\pm1.7\pm0.7$ MeV/$c^2$ and $30.7\pm5.5 \pm2.4$ MeV, respectively, which indicates the existence of a $p\bar{p}$ bound state.

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arXiv2024

Measurement of $e^{+}e^{-}\to ωη^{\prime}$ cross sections at $\sqrt{s}=$ 2.000 to 3.080 GeV

The Born cross sections for the process $e^{+}e^{-}\to ωη^{\prime}$ are measured at 22 center-of-mass energies from 2.000 to 3.080 GeV using data collected with the BESIII detector at the BEPCII collider. A resonant structure is observed with a statistical significance of 9.6$σ$. A Breit-Wigner fit determines its mass to be $M_R=(2153\pm30\pm31)~{\rm{MeV}}/c^{2}$ and its width to be $Γ_{R}=(167\pm77\pm7)~\rm{MeV}$, where the first uncertainties are statistical and the second are systematic.

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arXiv2024

Observation of $D^{+}\to K_{S}^{0}a_{0}(980)^{+}$ in the amplitude analysis of $D^{+} \to K_{S}^{0}π^+η$

We perform for the first time an amplitude analysis of the decay $D^{+}\to K_{S}^{0}π^+η$ and report the observation of the decay $D^{+}\to K_{S}^{0}a_{0}(980)^{+}$ using 2.93 fb$^{-1}$ of $e^+e^-$ collision data taken at a center-of-mass energy of 3.773 GeV with the BESIII detector. As the only W-annihilation free decay among $D$ to $a_{0}(980)$-pseudoscalar, $D^{+}\to K_{S}^{0}a_{0}(980)^{+}$ is the ideal decay to extract the contributions of the external and internal $W$-emission amplitudes involving $a_{0}(980)$ and study the final-state interactions. The absolute branching fraction of $D^{+}\to K_{S}^{0}π^+η$ is measured to be $(1.27\pm0.04_{\rm stat.}\pm0.03_{\rm syst.})\%$. The product branching fractions of $D^{+}\to K_{S}^{0}a_{0}(980)^{+}$ with $a_{0}(980)^{+}\to π^+η$ and $D^{+}\to π^+ K_0^*(1430)^0$ with $K_0^*(1430)^0\to K_{S}^{0}η$ are measured to be $(1.33\pm0.05_{\rm stat.}\pm0.04_{\rm syst.})\%$ and $(0.14\pm0.03_{\rm stat.}\pm0.01_{\rm syst.})\%$, respectively.

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arXiv2024

Observation of the semileptonic decays $D^0\rightarrow K_S^0\pi^-\pi^0 e^+ \nu_e$ and $D^+\rightarrow K_S^0\pi^+\pi^- e^+ \nu_e$

By analyzing $e^+e^-$ annihilation data corresponding to an integrated luminosity of 2.93 $\rm fb^{-1}$ collected at a center-of-mass energy of 3.773 GeV with the \text{BESIII} detector, the first observation of the semileptonic decays $D^0\rightarrow K_S^0\pi^-\pi^0 e^+ \nu_e$ and $D^+\rightarrow K_S^0\pi^+\pi^- e^+ \nu_e$ is reported. With a dominant hadronic contribution from $K_1(1270)$, the branching fractions are measured to be $\mathcal{B}(D^0\rightarrow {K}_1(1270)^-(\to K^0_S\pi^-\pi^0)e^+\nu_e)=(1.69^{+0.53}_{-0.46}\pm0.15)\times10^{-4}$ and $\mathcal{B}(D^+\to \bar{K}_1(1270)^0(\to K^0_S\pi^+\pi^-)e^+\nu_e)=(1.47^{+0.45}_{-0.40}\pm0.20)\times10^{-4}$ with statistical significance of 5.4$\sigma$ and 5.6$\sigma$, respectively. When combined with measurements of the $K_1(1270)\to K^+\pi^-\pi$ decays, the absolute branching fractions are determined to be $\mathcal{B}(D^0\to K_1(1270)^-e^+\nu_e)=(1.05^{+0.33}_{-0.28}\pm0.12\pm0.12)\times10^{-3}$ and $\mathcal{B}(D^+\to \bar{K}_1(1270)^0e^+\nu_e)=(1.29^{+0.40}_{-0.35}\pm0.18\pm0.15)\times10^{-3}$. The first and second uncertainties are statistical and systematic, respectively, and the third uncertainties originate from the assumed branching fractions of the $K_1(1270)\to K\pi\pi$ decays.

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arXiv2024

Measurement of $Λ$ transverse polarization in $e^{+}e^{-}$ collisions at $\sqrt{s}= 3.68-3.71$ GeV

With data samples collected with the BESIII detector at seven energy points at $\sqrt{s}= 3.68 - 3.71$ GeV, corresponding to an integrated luminosity of 333 pb$^{-1}$, we present a study of the $Λ$ transverse polarization in the $e^+e^-\toΛ\barΛ$ reaction. The significance of polarization by combining the seven energy points is found to be 2.6$σ$ including the systematic uncertainty, which implies a non-zero phase between the transition amplitudes of the $Λ\barΛ$ helicity states. The modulus ratio and the relative phase of EM-$psionic$ form factors combined with all energy points are measured to be $R^Ψ =$ 0.71$^{+0.10}_{-0.10}$ $\pm$ 0.03 and $ΔΦ^Ψ$ = (23$^{+8.8}_{-8.0}$ $\pm$ 1.6$)^\circ$, where the first uncertainties are statistical and the second systematic.

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arXiv2024

Determination of the $Σ^{+}$ Timelike Electromagnetic Form Factors

Based on data samples collected with the BESIII detector at the BEPCII collider, the process $e^{+}e^{-} \to Σ^{+}\barΣ^{-}$ is studied at center-of-mass energies $\sqrt{s}$ = 2.3960, 2.6454, and 2.9000 GeV. Using a fully differential angular description of the final state particles, both the relative magnitude and phase information of the $Σ^{+}$ electromagnetic form factors in the timelike region are extracted. The relative phase between the electric and magnetic form factors is determined to be $\sinΔΦ$ = -0.67~$\pm$~0.29~(stat)~$\pm$~0.18~(syst) at $\sqrt{s}$ = 2.3960 GeV, $ΔΦ$ = 55$^{\circ}$~$\pm$~19$^{\circ}$~(stat) $\pm$~14$^{\circ}$~(syst) at $\sqrt{s}$ = 2.6454 GeV, and 78$^{\circ}$~$\pm$~22$^{\circ}$~(stat) $\pm$~9$^{\circ}$~(syst) at $\sqrt{s}$ = 2.9000 GeV. For the first time, the phase of the hyperon electromagnetic form factors is explored in a wide range of four-momentum transfer. The evolution of the phase along with four-momentum transfer is an important input for understanding its asymptotic behavior and the dynamics of baryons.

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arXiv2024

Observation of $D^+_s\to η^\prime μ^+ν_μ$, Precision Test of Lepton Flavor Universality with $D^+_s\to η^{(\prime)} \ell^+ν_\ell$, and First Measurements of $D^+_s\to η^{(\prime)}μ^+ν_μ$ Decay Dynamics

By analyzing 7.33 fb$^{-1}$ of $e^+e^-$ annihilation data collected at center-of-mass energies between 4.128 and 4.226 GeV with the BESIII detector, we report the observation of the semileptonic decay $D^+_s\to η^\prime μ^+ν_μ$, with a statistical significance larger than 10$σ$, and the measurements of the $D_s^+ \to ημ^+ν_μ$ and $D_s^+ \to η^\primeμ^+ν_μ$ decay dynamics for the first time. The branching fractions of $D_s^+ \to ημ^+ν_μ$ and $D_s^+ \to η^\primeμ^+ν_μ$ are determined to be $(2.235\pm0.051_{\rm stat}\pm0.052_{\rm syst})\%$ and $(0.801\pm0.055_{\rm stat}\pm0.028_{\rm syst})\%$, respectively, with precision improved by factors of 6.0 and 6.6 compared to the previous best measurements. Combined with the results for the decays $D_s^+ \to ηe^+ν_e$ and $D_s^+ \to η^\prime e^+ν_e$, the ratios of the decay widths are examined both inclusively and in several $\ell^+ν_\ell$ four-momentum transfer ranges. No evidence for lepton flavor universality violation is found within the current statistics. The products of the hadronic form factors $f_{+,0}^{η^{(\prime)}}(0)$ and the $c\to s$ Cabibbo-Kobayashi-Maskawa matrix element $|V_{cs}|$ are determined. The results based on the two-parameter series expansion are $f^η_{+,0}(0)|V_{cs}| = 0.452\pm0.010_{\rm stat}\pm0.007_{\rm syst}$ and $f^{η^{\prime}}_{+,0}(0)|V_{cs}| = 0.504\pm0.037_{\rm stat}\pm0.012_{\rm syst}$, which help to constrain present models on $f_{+,0}^{η^{(\prime)}}(0)$. The forward-backward asymmetries are determined to be $\langle A_{\rm FB}^η\rangle=-0.059\pm0.031_{\rm stat}\pm0.005_{\rm syst}$ and $\langle A_{\rm FB}^{η^\prime}\rangle=-0.064\pm0.079_{\rm stat}\pm0.006_{\rm syst}$ for the first time, which are consistent with the theoretical calculation.

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arXiv2024

Study of light scalar mesons through $D_s^+ \to π^0 π^0 e^+ ν_e$ and $K_S^0 K_S^0 e^+ ν_e$ decays

Using 6.32~fb$^{-1}$ of $e^+e^-$ collision data recorded by the BESIII detector at center-of-mass energies between $4.178$ to $4.226$ GeV, we present the first measurement of the decay $D_s^+\to f_0(980)e^+ν_e,\,f_0(980)\to π^0π^0$. The product branching fraction of $D_s^+\to f_0(980)e^+ν_e,\,f_0(980)\to π^0π^0$ is measured to be $(7.9\pm1.4_{\rm stat} \pm0.3_{\rm syst})\times 10^{-4}$, with a statistical significance of $7.8σ$. Furthermore, the upper limits on the product branching fractions of $D_s^+\to f_0(500)e^+ν_e$ with $f_0(500)\to π^0π^0$ and the branching fraction of $D_s^+\to K_{S}^{0}K_{S}^{0}e^+ν_e$ are set to be $7.3\times 10^{-4}$ and $3.8\times 10^{-4}$ at 90\% confidence level, respectively. Our results provide valuable inputs to the understanding of the structures of light scalar mesons.

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arXiv2024

Search for the production of deuterons and antideuterons in e^+e^- annihilation at center-of-mass energies between 4.13 and 4.70 GeV

Using a data sample of $e^+e^-$ collision data corresponding to an integrated luminosity of 19 fb$^{-1}$ collected with the BESIII detector at the BEPCII collider, we search for the production of deuterons and antideuterons via $e^+e^-\to ppπ^-\bar{d}+c.c.$ for the first time at center-of-mass energies between 4.13 and 4.70 GeV. No significant signal is observed and the upper limit of the $e^+e^-\to ppπ^-\bar{d}+c.c.$ cross section is determined to be from 9.0 to 145 fb depending on the center-of-mass energy at the $90\%$ confidence level.

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arXiv2024

Search for the light hadron decay $χ_{c1}(3872) \to π^{+}π^{-}η$

With a data sample corresponding to an integrated luminosity of 11.5~fb$^{-1}$ collected with the BESIII detector operating at the BEPCII storage ring, for the first time the light hadron decay $χ_{c1}(3872) \rightarrow π^{+}π^{-}η$ is searched for. While no significant signal is observed, the upper limits at the 90\% confidence level for $σ[e^{+}e^{-} \rightarrow γχ_{c1}(3872)] \mathcal{B}[χ_{c1}(3872) \rightarrow π^{+}π^{-}η]$ at center-of-mass energies from 4.13 to 4.34 GeV are determined. By normalizing to the $χ_{c1}(3872)\toπ^+π^- J/ψ$ decay channel, a 90\% confidence level upper limit for the branching fraction ratio $\mathcal{R}=\mathcal{B}[χ_{c1}(3872) \rightarrowπ^{+}π^{-}η]/\mathcal{B}[χ_{c1}(3872) \rightarrow π^{+}π^{-} J/ψ] < 0.12$ is given. These measurements provide important inputs for understanding the internal structure of the $χ_{c1}(3872)$ resonance.

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