arXiv subjects

Y. Q. Fang

Publications and source records attributed to Y. Q. Fang.

At least 271 records · Page 15Linked to original sources

arXiv2024

Evidence of the $h_c\to K_S^0 K^+π^-+c.c.$ decay

Based on $(2.712\pm0.014)\times10^9$ $ψ(3686)$ events collected by the BESIII collaboration, evidence of the hadronic decay $h_c\to K_S^0K^+π^-+c.c.$ is found with a significance of $4.3σ$ in the $ψ(3686)\toπ^0 h_c$ process. The branching fraction of $h_c\to K_S^0 K^+π^- +c.c.$ is measured to be $(7.3\pm0.8\pm1.8)\times10^{-4}$, where the first and second uncertainties are statistical and systematic, respectively. Combining with the exclusive decay width of $η_c\to K\bar{K}π$, our result indicates inconsistencies with both pQCD and NRQCD predictions.

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arXiv2024

Amplitude Analysis of the Decays $D^0\toπ^+π^-π^+π^-$ and $π^+π^-π^0π^0$

Using $e^+e^-$ annihilation data corresponding to an integrated luminosity of 2.93 $\rm fb^{-1}$ taken at the center-of-mass energy $\sqrt{s}=3.773$~GeV with the BESIII detector, a joint amplitude analysis is performed on the decays $D^0\toπ^+π^-π^+π^-$ and $D^0\toπ^+π^-π^0π^0$(non-$η$). The fit fractions of individual components are obtained, and large interferences among the dominant components of $D^{0}\to a_{1}(1260)π$, $D^{0}\toπ(1300)π$, $D^{0}\toρ(770)ρ(770)$ and $D^{0}\to2(ππ)_{S}$ are found in both channels. With the obtained amplitude model, the $CP$-even fractions of $D^0\to π^+π^-π^+π^-$ and $D^0\toπ^+π^-π^0π^0$(non-$η$) are determined to be $(75.2\pm1.1_{\rm stat.}\pm1.5_{\rm syst.})\%$ and $(68.9\pm1.5_{\rm stat.}\pm 2.4_{\rm syst.})\%$, respectively. The branching fractions of $D^0\to π^+π^-π^+π^-$ and $D^0\toπ^+π^-π^0π^0$(non-$η$) are measured to be $(0.688\pm0.010_{\rm stat.}\pm 0.010_{\rm syst.})\%$ and $(0.951\pm0.025_{\rm stat.}\pm 0.021_{\rm syst.})\%$, respectively. The amplitude analysis provides an important model for binning strategy in the measurements of the strong phase parameters of $D^0 \to 4π$ when used to determine the CKM angle $γ(ϕ_{3})$ via the $B^{-}\to D K^{-}$ decay.

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arXiv2024

First observation of the decay $Λ^+_c\to nK^{0}_{S}π^+π^0$

Based on 4.5 fb$^{-1}$ of $e^{+}e^{-}$ collision data accumulated at center-of-mass energies between $4599.53$ MeV and $4698.82$ MeV with the BESIII detector, the decay $Λ_{c}^{+}\to nK_{S}^{0}π^+π^0$ is observed for the first time with a significance of $9.2σ$. The branching fraction is measured to be $(0.85\pm0.13\pm0.03)\%$, where the first uncertainty is statistical and the second systematic, which differs from the theoretical prediction based on isospin by 4.4$σ$. This indicates that there may be resonant contributions or some unknown dynamics in this decay.

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arXiv2024

Precise measurement of the $e^+e^-\to D_s^+D_s^-$ cross sections at center-of-mass energies from threshold to 4.95 GeV

Using the $e^+e^-$ collision data collected with the BESIII detector operating at the BEPCII collider, at center-of-mass energies from the threshold to $4.95$~GeV, we present precise measurements of the cross sections for the process $e^+e^-\to D_s^+D_s^-$ using a single tag method. The resulting cross section lineshape exhibits several new structures, thereby offering an input for coupled channel analysis and model tests, which are critical to understand vector charmonium-like states with masses between 4 and 5~GeV.

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arXiv2024

Observation of the decay $h_{c}\to3(π^{+}π^{-})π^{0}$

Based on $(2712.4\pm14.1)\times10^{6}$ $ψ(3686)$ events collected with the BESIII detector, we study the decays $h_{c}\to3(π^{+}π^{-})π^{0}$, $h_{c}\to2(π^{+}π^{-})ω$, $h_{c}\to2(π^{+}π^{-})π^{0}η$, $h_{c}\to2(π^{+}π^{-})η$, and $h_{c}\to p\bar{p}$ via $ψ(3686)\toπ^{0}h_{c}$. The decay channel $h_{c}\to3(π^{+}π^{-})π^{0}$ is observed for the first time, and its branching fraction is determined to be $\left( {9.28\pm 1.14 \pm 0.77} \right) \times {10^{ - 3}}$, where the first uncertainty is statistical and the second is systematic. In addition, first evidence is found for the modes $h_{c} \to 2(π^{+}π^{-})π^{0}η$ and $h_{c}\to2(π^{+}π^{-})ω$ with significances of 4.8$σ$ and 4.7$σ$, and their branching fractions are determined to be $(7.55\pm1.51\pm0.77)\times10^{-3}$ and $\left( {4.00 \pm 0.86 \pm 0.35}\right) \times {10^{ - 3}}$, respectively. No significant signals of $h_c\to 2(π^+π^-)η$ and $h_{c}\to p\bar{p}$ are observed, and the upper limits of the branching fractions of these decays are determined to be $<6.19\times10^{-4}$ and $<4.40\times10^{-5}$ at the 90% confidence level, respectively.

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arXiv2024

Observation of $ψ(3686)\to 3ϕ$

Using $(2.712\pm0.014)\times 10^9$ $ψ(3686)$ events collected by the BESIII detector operating at the BEPCII collider, we report the first observation of $ψ(3686)\to 3ϕ$ decay with a significance larger than 10$σ$. The branching fraction of this decay is determined to be $(1.46\pm0.05\pm0.17)\times10^{-5}$, where the first uncertainty is statistical and the second is systematic. No significant structure is observed in the $ϕϕ$ invariant mass spectra.

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arXiv2024

First observation of $Λ_c^+\rightarrowΛK^+π^0$ and evidence of $Λ_c^+\rightarrowΛK^+π^+π^-$

We present the first observation of the singly Cabibbo-suppressed decay $Λ_c^+ \rightarrow ΛK^+π^0$ with a significance of $5.7σ$ and the first evidence of $Λ_c^+ \rightarrow ΛK^+π^+π^-$ decay with a significance of $3.1σ$, based on $e^+e^-$ annihilation data recorded by the BESIII detector at the BEPCII collider. The data correspond to an integrated luminosity of $6.4~{\rm fb^{-1}}$, in the center-of-mass energy range from $4.600~{\rm GeV}$ to $4.950~{\rm GeV}$. We determine the branching fractions of $Λ_c^+ \rightarrow ΛK^+π^0$ and $Λ_c^+ \rightarrow ΛK^+π^+π^-$ relative to their Cabibbo-favored counterparts to be $\frac{\mathcal{B}(Λ_c^+ \rightarrow ΛK^+π^0)}{\mathcal{B}(Λ_c^+ \rightarrow Λπ^+π^0)} = (2.09\pm0.39_{\mathrm{stat.}}\pm0.07_{\mathrm{syst.}}) \times 10^{-2}$ and $\frac{\mathcal{B}(Λ_c^+ \rightarrow ΛK^+π^+π^-)}{\mathcal{B}(Λ_c^+ \rightarrow Λπ^+π^+π^-)} = (1.13\pm0.41_{\mathrm{stat.}}\pm0.06_{\mathrm{syst.}}) \times 10^{-2}$, respectively. Moreover, by combining our measured result with the world average of $\mathcal{B}(Λ^+_c\to Λπ^+π^0)$, we obtain the branching fraction $\mathcal{B}(Λ_c^+ \to ΛK^+π^0) = (1.49\pm0.27_{\mathrm{stat.}}\pm0.05_{\mathrm{syst.}}\pm0.08_{\mathrm{ref.}}) \times 10^{-3}$. This result significantly departs from theoretical predictions based on quark $SU(3)$ flavor symmetry, which is underpinned by the presumption of meson pair $S$-wave amplitude dominance.

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arXiv2024

Search for a muonphilic scalar $X_{0}$ or vector $X_{1}$ via $J/ψ\toμ^+μ^-+\rm{invisible}$ decays at BESII

A light scalar $X_{0}$ or vector $X_{1}$ particles have been introduced as a possible explanation for the $(g-2)_μ$ anomaly and dark matter phenomena. Using $(8.998\pm 0.039)\times10^9$ $\jpsi $ events collected by the BESIII detector, we search for a light muon philic scalar $X_{0}$ or vector $X_{1}$ in the processes $J/ψ\toμ^+μ^- X_{0,1}$ with $X_{0,1}$ invisible decays. No obvious signal is found, and the upper limits on the coupling $g_{0,1}'$ between the muon and the $X_{0,1}$ particles are set to be between $1.1\times10^{-3}$ and $1.0\times10^{-2}$ for the $X_{0,1}$ mass in the range of $1<M(X_{0,1})<1000$ MeV$/c^2$ at 90$\%$ confidence level.

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arXiv2024

Measurement of the Electromagnetic Transition Form-factors in the decays $η'\rightarrowπ^+π^-l^+l^-$

With a sample of $(10087\pm44)\times10^{6}$ $J/ψ$ events accumulated with the BESIII detector, we analyze the decays $η'\rightarrowπ^+π^-l^+l^-(l=e,$ $μ)$ via the process $J/ψ\rightarrowγη'$. The branching fractions are measured to be $\mathcal{B}(η'\rightarrowπ^+π^-e^+e^-)=(2.45\pm0.02(\rm{stat.})\pm0.08(\rm{syst.})) \times10^{-3}$ and $\mathcal{B}(η'\rightarrowπ^+π^-μ^+μ^-)=(2.16\pm0.12(\rm{stat.})\pm0.06(\rm{syst.}))\times10^{-5}$, and the ratio is $\frac{\mathcal{B}(η'\rightarrowπ^{+}π^{-}e^{+}e^{-})}{\mathcal{B}(η'\rightarrowπ^{+}π^{-}μ^{+}μ^{-})} = 113.4\pm0.9(\rm{stat.})\pm3.7(\rm{syst.})$. In addition, by combining the $η'\rightarrowπ^+π^-e^+e^-$ and $η'\rightarrowπ^+π^-μ^+μ^-$ decays, the slope parameter of the electromagnetic transition form factor is measured to be $b_{η'}=1.30\pm0.19\ (\mathrm{GeV}/c^{2})^{-2}$, which is consistent with previous measurements from BESIII and theoretical predictions from the VMD model. The asymmetry in the angle between the $π^+π^-$ and $l^+l^-$ decay planes, which has the potential to reveal the $CP$-violation originating from an unconventional electric dipole transition, is also investigated. The asymmetry parameters are determined to be $\mathcal{A}_{CP}(η'\rightarrowπ^+π^-e^+e^-)=(-0.21\pm0.73(\rm{stat.})\pm0.01(\rm{syst.}))\%$ and $\mathcal{A}_{CP}(η'\rightarrowπ^+π^-μ^+μ^-)=(0.62\pm4.71(\rm{stat.})\pm0.08(\rm{syst.}))\%$, implying that no evidence of $CP$-violation is observed at the present statistics. Finally, an axion-like particle is searched for via the decay $η'\rightarrowπ^+π^-a, a\rightarrow e^+e^-$, and upper limits of the branching fractions are presented for the mass assumptions of the axion-like particle in the range of $0-500\ \mathrm{MeV}/c^{2}$.

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arXiv2024

Study of $e^{+}e^{-}\rightarrowπ^{+}π^{-}π^{0}$ at $\sqrt{s}$ from 2.00 to 3.08 GeV at BESIII

With the data samples taken at center-of-mass energies from 2.00 to 3.08 GeV with the BESIII detector at the BEPCII collider, a partial wave analysis on the $e^{+}e^{-}\rightarrowπ^{+}π^{-}π^{0}$ process is performed. The Born cross sections for $e^{+}e^{-}\rightarrowπ^{+}π^{-}π^{0}$ and its intermediate processes $e^{+}e^{-}\rightarrowρπ$ and $ρ(1450)π$ are measured as functions of $\sqrt{s}$. The results for $e^{+}e^{-}\rightarrowπ^{+}π^{-}π^{0}$ are consistent with previous results measured with the initial state radiation method within one standard deviation, and improve the uncertainty by a factor of ten. By fitting the line shapes of the Born cross sections for the $e^{+}e^{-}\rightarrowρπ$ and $ρ(1450)π$, a structure with mass $M = 2119\pm11\pm15\ {\rm MeV}/c^2$ and width $Γ=69\pm30\pm5 {\rm MeV}$ is observed with a significance of $5.9σ$, where the first uncertainties are statistical and the second ones are systematic. This structure can be intepreteted as an excited $ω$ state.

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arXiv2024

First Measurement of the Decay Asymmetry in the pure W-boson-exchange Decay $Λ_{c}^{+}\toΞ^{0}K^{+}$

Based on $4.4~\text{fb}^{-1}$ of $e^{+}e^{-}$ annihilation data collected at the center-of-mass energies between $4.60$ and $4.70~\text{GeV}$ with the BESIII detector at the BEPCII collider, the pure \textit{W}-boson-exchange decay $Λ_{c}^{+}\toΞ^{0}K^{+}$ is studied with a full angular analysis. The corresponding decay asymmetry is measured for the first time to be $α_{Ξ^{0}K^{+}}=0.01\pm0.16({\rm stat.})\pm0.03({\rm syst.})$. This result reflects the non-interference effect between the $S$- and $P$-wave amplitudes. The phase shift between $S$- and $P$-wave amplitudes has two solutions, which are $δ_{p}-δ_{s}=-1.55\pm0.25({\rm stat.})\pm0.05({\rm syst.})~\text{rad}$ or $1.59\pm0.25({\rm stat.})\pm0.05({\rm syst.})~\text{rad}$.

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arXiv2024

First measurements of the absolute branching fraction of $Λ_{c}(2625)^{+}\to Λ^{+}_{c}π^+π^-$ and upper limit on $Λ_{c}(2595)^{+}\to Λ^{+}_{c}π^+π^-$

The absolute branching fraction of the decay $Λ_{c}(2625)^{+}\to Λ^{+}_{c}π^+π^-$ is measured for the first time to be $(50.7 \pm 5.0_{\rm{stat.}} \pm 4.9_{\rm{syst.}} )\%$ with 368.48 pb$^{-1}$ of $e^+e^-$ collision data collected by the BESIII detector at the center-of-mass energies of $\sqrt{s} = 4.918$ and $4.950$ GeV. This result is lower than the naive prediction of 67\%, obtained from isospin symmetry, by more than $2σ$, thereby indicating that the novel mechanism referred to as the \textit{threshold effect}, proposed for the strong decays of $Λ_{c}(2595)^{+}$, also applies to $Λ_{c}(2625)^{+}$. This measurement is necessary to obtain the coupling constants for the transitions between $s$-wave and $p$-wave charmed baryons in heavy hadron chiral perturbation theory. In addition, we search for the decay $Λ_{c}(2595)^{+}\to Λ^{+}_{c}π^+π^-$. No significant signal is observed, and the upper limit on its branching fraction is determined to be 80.8\% at the 90\% confidence level.

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arXiv2023

Observation of $χ_{cJ}\to 3(K^+K^-)$

By analyzing $(27.12\pm0.14)\times10^8$ $ψ(3686)$ events collected with the BESIII detector operating at the BEPCII collider, the decay processes $χ_{cJ} \to 3(K^+K^-)$ ($J=0,1,2$) are observed for the first time with statistical significances of 8.2$σ$, 8.1$σ$, and 12.4$σ$, respectively. The product branching fractions of $ψ(3686)\toγχ_{cJ}$, $χ_{cJ}\to 3(K^+K^-)$ are presented and the branching fractions of $χ_{cJ}\to 3(K^+K^-)$ decays are determined to be $\mathcal{B}_{χ_{c0}\to 3(K^+K^-)}$=$(10.7\pm1.8\pm1.1)$$\times10^{-6}$, $\mathcal{B}_{χ_{c1}\to 3(K^+K^-)}$=$(4.2\pm0.9\pm0.5)$$\times10^{-6}$, and $\mathcal{B}_{χ_{c2}\to 3(K^+K^-)}$=$(7.2\pm1.1\pm0.8)$$\times10^{-6}$, where the first uncertainties are statistical and the second are systematic.

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arXiv2023

Measurements of $Σ$ electromagnetic form factors in the time-like region using the untagged initial-state radiation technique

The process $e^{+}e^{-}\toΣ^{+}\barΣ^{-}$ is studied from threshold up to 3.04 GeV/$c^2$ via the initial-state radiation technique using data with an integrated luminosity of 12.0 fb$^{-1}$, collected at center-of-mass energies between 3.773 and 4.258 GeV with the BESIII detector at the BEPCII collider. The pair production cross sections and the effective form factors of $Σ$ are measured in eleven $Σ^{+}\barΣ^{-}$ invariant mass intervals from threshold to 3.04 GeV/$c^2$. The results are consistent with the previous results from Belle and BESIII. Furthermore, the branching fractions of the decays $J/ψ\toΣ^{+}\barΣ^{-}$ and $ψ(3686)\toΣ^{+}\barΣ^{-}$ are determined and the obtained results are consistent with the previous results of BESIII.

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arXiv2023

Observation of significant flavor-SU(3) breaking in the kaon wave function at $12~{\rm GeV}^2<Q^2<25~{\rm GeV}^2$ and discovery of the charmless decay $ψ(3770)\to K_S^0K_L^0$

We present cross sections for the reaction $e^+e^-\to K_S^0K_L^0$ at center-of-mass energies ranging from 3.51 GeV to 4.95 GeV using data samples collected in the BESIII experiment, corresponding to a total integrated luminosity of 26.5 fb$^{-1}$. The ratio of neutral-to-charged kaon form factors at large momentum transfers ($12~{\rm GeV}^2<Q^2<25~{\rm GeV}^2$) is determined to be $0.21\pm 0.01$, which indicates a small but significant effect of flavor-SU(3) breaking in the kaon wave function, and consequently excludes the possibility that flavor-SU(3) breaking is the primary reason for the strong experimental violation of the pQCD prediction $|F(π^{\pm})|/|F(K^{\pm})|=f^2_π/f^2_{K}$, where $F(π^{\pm})$ and $F(K^{\pm})$ are the form factors, and $f_π$ and $f_{K}$ are the decay constants of charged pions and kaons, respectively. We also observe a significant signal for the charmless decay $ψ(3770)\to K_S^0K_L^0$ for the first time. Within a $1σ$ contour of the likelihood value, the the branching fraction for $ψ(3770)\to K_S^0K_L^0$ is determined to be ${\cal B}=(2.63_{-1.59}^{+1.40})\times 10^{-5}$, and the relative phase between the continuum and $ψ(3770)$ amplitudes is $ϕ=(-0.39_{-0.10}^{+0.05})π$. The branching fraction is in good agreement with the $\mathcal{S}$- and $\mathcal{D}$-wave charmonia mixing scheme proposed in the interpretation of the "$ρπ$ puzzle" between $J/ψ$ and $ψ(3686)$ decays.

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arXiv2023

Search for $D^{0}\to K_{S}^{0} K^{-} e^{+}ν_{e}$, $D^{+}\to K_{S}^{0} K_{S}^{0} e^{+}ν_{e}$, and $D^{+}\to K^{+}K^{-} e^{+}ν_{e}$

A search has been performed for the semileptonic decays $D^{0}\to K_{S}^{0} K^{-} e^{+}ν_{e}$, $D^{+}\to K_{S}^{0} K_{S}^{0} e^{+}ν_{e}$ and $D^{+}\to K^{+}K^{-} e^{+}ν_{e}$, using $7.9~\mathrm{fb}^{-1}$ 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 are set at the 90\% confidence level of $2.13\times10^{-5}$, $1.54\times10^{-5}$ and $2.10\times10^{-5}$ for the branching fractions of $D^{0}\to K_{S}^{0} K^{-} e^{+}ν_{e}$, $D^{+}\to K_{S}^{0} K_{S}^{0} e^{+}ν_{e}$ and $D^{+}\to K^{+}K^{-} e^{+}ν_{e}$, respectively.

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arXiv2023

Measurement of the cross sections for $e^+e^-\toηπ^+π^-$ at center-of-mass energies between 2.00 and 3.08 GeV

Using data samples collected at center-of-mass energies between 2.000 and 3.080 GeV with the BESIII detector operating at the BEPCII collider, a partial-wave analysis is performed on the process $e^+e^-\toηπ^+π^-$. In addition to the dominant $e^+e^-\toρη$ component, the $e^+e^-\to a_2(1320)π$ process is also sizeable, contributing up to 24% of the total reaction. The measured cross sections of the process $e^+e^-\toηπ^+π^-$ are systematically higher than those of BaBar by more than $3σ$ at center-of-mass energies between 2.000 and 2.300 GeV. In the cross section lineshape for $e^+e^-\to a_2(1320)π$, a resonant structure is observed with a significance of $5.5σ$, with $M=(2044\pm31\pm4)$ MeV/$c^2$, $Γ=(163\pm69\pm24)$ MeV and $\mathcal{B_{R}}\cdotΓ_{e^+e^-}^{R}=(34.6\pm17.1\pm6.0)$ eV or $(137.1\pm73.3\pm2.1)$ eV. In the cross section lineshape for $e^+e^-\toρη$, an evidence of a dip structure around 2180 MeV/$c^2$ is observed with statistical significance of $3.0σ$.

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arXiv2023

Improved measurement of the decays $η' \to π^{+}π^{-}π^{+(0)}π^{-(0)}$ and search for the rare decay $η' \to 4π^{0}$

Using a sample of 10 billion $J/ψ$ events collected with the BESIII detector, the decays $η' \to π^{+}π^{-}π^{+}π^{-}$, $η' \to π^{+}π^{-}π^{0}π^{0}$ and $η' \to 4 π^{0}$ are studied via the process $J/ψ\toγη'$. The branching fractions of $η' \to π^{+}π^{-}π^{+}π^{-}$ and $η' \to π^{+}π^{-}π^{0}$ $π^{0}$ are measured to be $( 8.56 \pm 0.25({\rm stat.}) \pm 0.23({\rm syst.}) ) \times {10^{ - 5}}$ and $(2.12 \pm 0.12({\rm stat.}) \pm 0.10({\rm syst.})) \times {10^{ - 4}}$, respectively, which are consistent with previous measurements but with improved precision. No significant $η' \to 4 π^{0}$ signal is observed, and the upper limit on the branching fraction of this decay is determined to be less than $1.24 \times {10^{-5}}$ at the $90\%$ confidence level. In addition, an amplitude analysis of $η' \to π^{+}π^{-}π^{+}π^{-}$ is performed to extract the doubly virtual isovector form factor $α$ for the first time. The measured value of $α=1.22 \pm 0.33({\rm stat.}) \pm 0.04({\rm syst.})$, is in agreement with the prediction of the VMD model.

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