arXiv subjects

Yu-Fei Wang

Publications and source records attributed to Yu-Fei Wang.

At least 19 recordsLinked to original sources

arXiv2026

Baryon Transition Form Factors from Dynamical Coupled-Channel Analyses

In this talk, the electromagnetic transition form factors from the nucleon ground state to twelve $N^*$ and $\Delta$ states are exhibited and discussed. Those results are extracted through a comprehensive coupled-channel approach -- the Juelich-Bonn-Washington model, with the center-of-mass energy ranging from $1.13$ GeV to $1.8$ GeV, and the photon virtuality up to $8$ GeV$^2$. The extraction is based on $10^5$ electroproduction data points of $\pi N$, $\eta N$, and $K\Lambda$ channels, with additionally about $5\times 10^4$ data points in the hadronic sector as well as photoproductions as boundary conditions. The form factors are defined from the residues at the corresponding resonance poles in the multipole amplitudes. Uncertainties are also estimated by the exploration of the parameter space. The qualitative behavior of the transition form factors of $N(1440)$ and $\Delta(1232)$ here are in agreement with the previous studies, while for the other states, there has not been literature results that are also defined at the resonance poles.

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arXiv2025

Sifting out the neutral and charged components of $X(3872)$ from a spin observable

In this work, we propose a new method to detect the composition of the $X(3872)$ state. Based on a widely accepted interpretation that $X(3872)$ is a weakly bound $S$-wave molecule of the $D^{*0} \bar{D}^{0}$ (neutral) and $D^{*+} D^{-}$ (charged) configurations, the process $X(3872) \to \bar{D}^{*0} D^0$ is described by one-loop triangle diagrams with the corresponding components as intermediate particles, and with the parameters constrained by the experimental branching ratio. Unlike the mild behavior of the neutral component, the charged component manifests itself as a distinct structure near the $D^{*+} D^{-}$ threshold at $3.880$ GeV, in the $M_{\bar{D}^{*0} D^0}$ invariant mass distribution of the spin density matrix element $\rho^{D^*}_{00}$. Hence the line shape of $\rho^{D^*}_{00}$ near this structure depends sensitively on the proportions of the two configurations. We propose high-precision measurements of this matrix element by future BESIII and Belle experiments to elucidate how a molecular $X(3872)$ state is composed.

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arXiv2025

Effects of hadronic molecule $N(2080)3/2^-$ on $K^{*+}\Lambda$ photoproduction

In our previous work [Phys. Rev. C {\bf 101}, 014003 (2020)], we have analyzed all available data on differential cross sections and spin density matrix elements for the $\gamma p \to K^{\ast +} \Lambda$ reaction using an effective Lagrangian approach. There, the $t$-channel $K$, $K^*$, and $\kappa$ exchanges, the $u$-channel $\Lambda$, $\Sigma$, and $\Sigma^*$ exchanges, the $s$-channel $N$, $N(2060)5/2^-$, and $N(2000)5/2^+$ exchanges, and the interaction current were taken into account in constructing the reaction amplitudes. It was found that, overall, the agreement of the theoretical results with the corresponding data is fairly good. However, noticeable discrepancies between the model results and the data on spin density matrix elements $\rho_{00}$ are still observed in the center-of-mass energy region around $W \approx 2.08$ GeV, indicating the need for additional reaction mechanisms. On the other hand, the hidden-strange pentaquark-like state $N(2080)3/2^-$, which is proposed to be a $K^*\Sigma$ molecular state as the strange partner of $P_c(4457)$ hadronic molecule, has been found to play quite active roles in reproducing the data for $K^{*+}\Sigma^0$, $K^{*0}\Sigma^+$, and $\phi p$ photoproduction reactions. Based on these observations, in the present work, we reanalyze the data for the $\gamma p \to K^{\ast +} \Lambda$ reaction by incorporating the pentaquark-like state $N(2080)3/2^-$ in our previously proposed model. The results show that with the inclusion of the contributions of $N(2080)3/2^-$, the quality of the theoretical description of the $\gamma p \to K^{*+}\Lambda$ data can be considerably improved.

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arXiv2025

Nature of the $P_c$ states from compositeness criteria

Based on a coupled-channel approach, we investigate the structures of four $P_c$ states through compositeness criteria. Toward a more precise description of the states, we have obtained refined fit results of the LHCb data on the $J/\psi p$ invariant mass distribution of the $\Lambda_b^0\to J/\psi p K^-$ decay. Allowing for the fact that each of the four $P_c$ states couples strongly to a nearby $S$-wave channel, three criteria on the compositeness/elementariness are adopted in this study: the pole-counting rule, the spectral density function, and the Gamow wave function. Compositeness information is extracted from the scattering amplitudes and the pole parameters (pole positions and residues), without any preconceived assumptions on the nature of the $P_c$ states, and without any dependence on the model parametrization. Consistently within the framework of all the three methods, it has been found that the $P_c(4312)\,1/2^-$ is mainly composed by $\bar{D}\Sigma_c$, $P_c(4380)\,3/2^-$ by $\bar{D}\Sigma_c^*$, while the $P_c(4440)\,1/2^-$ and $P_c(4457)\,3/2^-$ states both turn out as composite states of $\bar{D}^*\Sigma_c$. The upper limits of the values of their elementariness are estimated to be rather small. This paper provides an additional confirmation of the molecular interpretation for the $P_c$ states in the literature.

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arXiv2024

Search for the $\Sigma(1380)1/2^-$ state in $\Lambda^+_c \to \gamma \pi^+ \Lambda$ decay by triangle singularity

In this work, we investigate the resonance production in $\Lambda^+_c \to \gamma \pi^+ \Lambda$ decay through the triangle singularity (TS) mechanism, within an effective Lagrangian approach. We find that the appropriate loop decay process could develop a triangle singularity in the invariant mass $M_{\pi\Lambda}$ around $1.35$ GeV, with the shape depending on the quantum numbers of $\Sigma^*$ states that couple to the final $\pi\Lambda$ system. Especially, the $\Sigma(1380)1/2^-$ state newly predicted in the pentaquark model, if exists, significantly enhances the TS contribution and sharpens the TS peak due to the $S$-wave $\Sigma^*\pi\Sigma$ vertex in the loop. Therefore, the existence of the $\Sigma(1380)1/2^-$ state can be examined by measuring the TS signal in $\Lambda^+_c \to \gamma \pi^+ \Lambda$. Considering also possible tree-level diagrams, we additionally obtain the branching ratio ${\rm Br}(\Lambda^+_c \to \gamma \pi^+ \Lambda)\simeq 1.5\times 10^{-5}$. We suggest the investigation of this reaction by future BESIII, LHCb, and Belle experiments.

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arXiv2024

Exploration of the LHCb $P_c$ states and possible resonances in a unitary coupled-channel model

We extend our previous study of the interactions of $\bar{D}^{(*)} Λ_c - \bar{D}^{(*)}Σ_c^{(*)}$ within an analytic, unitary, coupled-channel approach by including the $J/ψp$ channel and performing fits to the $J/ψp$ invariant mass distributions in the $Λ_b^0 \to J/ψp K^-$ decay by the LHCb Collaboration. We take into account the contributions of $t$-channel pseudoscalar and vector meson exchanges and $u$-channel baryon exchanges in this work, and a series of bound states and resonances with different spin-parities are dynamically generated. According to the results, four states have a significant impact on the physical observables, with two having a spin-parity of $1/2^-$ and the other two having $3/2^-$. These states can be associated with the LHCb hidden-charm pentaquarks. We further provide the coupling strength between each pole and different channels, which provides some insights on how to search for them in future experiments. Moreover, we also search for poles in higher partial waves up to $J=7/2$ and find indications for the existence of several states with larger widths.

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arXiv2024

Global Data-Driven Determination of Baryon Transition Form Factors

Hadronic resonances emerge from strong interactions encoding the dynamics of quarks and gluons. The structure of these resonances can be probed by virtual photons parameterized in transition form factors. In this study, twelve $N^*$ and $\Delta$ transition form factors at the pole are extracted from data with the center-of-mass energy from $\pi N$ threshold to $1.8\,{\rm GeV}$, and the photon virtuality $0\leq Q^2/{\rm GeV}^2\leq 8$. For the first time, these results are determined from a simultaneous analysis of more than one state, i.e., $\sim 10^5$ $\pi N$, $\eta N$, and $K\Lambda$ electroproduction data. In addition, about $ 5\cdot 10^4$ data in the hadronic sector as well as photoproduction serve as boundary conditions. For the $\Delta(1232)$ and $N(1440)$ states our results are in qualitative agreement with previous studies, while the transition form factors at the poles of some higher excited states are estimated for the first time. Realistic uncertainties are determined by further exploring the parameter space.

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arXiv2024

The reaction $πN \to ωN$ in a dynamical coupled-channel approach

This talk is on a refined investigation on light flavor meson-baryon scatterings, using a dynamical coupled-channel approach, i.e. the Jülich-Bonn model. The previous channel space of $πN$, $πΔ$, $σN$, $ρN$, $ηN$, $K Λ$ and $K Σ$ is extended by adding the $ωN$ final state. The spectra of $N^*$ and $Δ$ resonances are extracted, based on the result of a global fit to a worldwide collection of data, in the energy region from the $πN$ threshold to center-of-mass energy $z=2.3$ GeV (approximately $300$ parameters against $9000$ data points). A negative value of the $ωN$ elastic spin-averaged scattering length has been extracted.

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arXiv2024

Nature of the $N^*$ and $Δ$ resonances via coupled-channel dynamics

This work aims at determining the composition of certain $N^*$ and $Δ$ resonances, i.e. whether they are compact states formed directly by quarks and gluons, or hadronic molecules generated from the meson-baryon interaction. The information of the resonance poles is provided by a comprehensive coupled-channel approach, the Jülich-Bonn model. $13$ states that are significant in this approach are studied. Two criteria for each state are adopted in this paper, the comparison thereof roughly indicates the model uncertainties. It is found that the conclusions for $8$ resonances are relatively certain: $N(1535) \frac{1}{2}^-$, $N(1440) \frac{1}{2}^+$, $N(1710) \frac{1}{2}^+$, and $N(1520) \frac{3}{2}^-$ tend to be composite; whereas $N(1650) \frac{1}{2}^-$, $N(1900) \frac{3}{2}^+$, $N(1680) \frac{5}{2}^+$, and $Δ(1600) \frac{3}{2}^+$ tend to be compact.

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arXiv2024

On the nature of the $N^*$ and $Δ$ resonances via coupled-channel dynamics

This talk focuses on a recent work aiming at determining the composition of certain $N^*$ and $Δ$ resonances, i.e. whether they are compact states formed directly by quarks and gluons, or composite generated from the meson-baryon interaction. The information of the resonance poles is provided by a comprehensive coupled-channel approach, the Jülich-Bonn model. Thirteen states that are significant in this approach are studied. Two criteria for each state are adopted in this paper, the comparison thereof roughly indicates the model uncertainties. It is found that the conclusions for eight resonances are relatively certain: $N(1535) \frac{1}{2}^-$, $N(1440) \frac{1}{2}^+$, $N(1710) \frac{1}{2}^+$, and $N(1520) \frac{3}{2}^-$ tend to be composite; whereas $N(1650) \frac{1}{2}^-$, $N(1900) \frac{3}{2}^+$, $N(1680) \frac{5}{2}^+$, and $Δ(1600) \frac{3}{2}^+$ tend to be compact.

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arXiv2022

The reaction $πN \to ωN$ in a dynamical coupled-channel approach

A refined investigation on light flavor meson-baryon scatterings is performed using a dynamical coupled-channel approach, the Jülich-Bonn model, that respects unitartiy and analyticity constraints. The channel space of $πN$, $πΔ$, $σN$, $ρN$, $ηN$, $K Λ$ and $K Σ$ is extended by adding the $ωN$ final state. The spectra of $N^*$ and $Δ$ resonances are extracted in terms of complex poles of the scattering amplitudes, based on the result of a global fit to a worldwide collection of data, in the energy region from the $πN$ threshold to center-of-mass energy $z=2.3$ GeV. A negative value of the $ωN$ elastic spin-averaged scattering length is extracted, questioning the existence of bound states of the $ω$ meson in the nuclear matter.

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arXiv2021

An $N/D$ study of the $S_{11}$ channel $πN$ scattering amplitude

Extensive dynamical $N/D$ calculations are made in the study of $S_{11}$ channel low energy $π$N scatterings, based on various phenomenological model inputs of left cuts at tree level. The subtleties of the singular behavior of the partial wave amplitude at the origin of the complex $s$ plane are carefully analysed. Furthermore, { it is found that the dispersion representation for the phase shift, $δ$, has to be modified in the case of $π$N scatterings. An additional contribution from the dispersion integral exists, which is, however, almost exactly cancelled the contribution from two virtual poles located near the end points of the segment cut induced by $u$ channel nucleon exchanges.} Relying very little on the details of the dynamical inputs, the subthreshold resonance $N^*(890)$ survives.

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arXiv2020

How does the $S_{11}$ $N^*(890)$ state emerge from a naive $K$ matrix fit?

We give a pedagogical analysis on $K$ matrix models describing the $πN$ scattering amplitude, in $S_{11}$ channel at low energies. We show how the correct use of analyticity in the $s$ channel and crossing symmetry in $t$ and $u$ channels leads to a much improved analytic behavior in the negative $s$ region, in agreement with the prediction from chiral perturbation amplitudes in its validity region. The analysis leads again to the conclusion that a genuine $N^*(890)$ resonance exists.

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arXiv2019

Discussions on the Line-shape of $X(4660)$ Resonance

A careful reanalysis is made on $e^+e^-\to X(4660)\to (Λ_c\barΛ_c)/(ψ'ππ)$ processes, aiming at resolving the apparent conflicts between Belle and BESIII data above $Λ_c\barΛ_c$ threshold. We use a model containing a Breit-Wigner resonance and $Λ_c\barΛ_c$ four-point contact interactions, with which the enhancement right above the $Λ_c\barΛ_c$ threshold is well explained by a virtual pole generated by $Λ_c\barΛ_c$ attractive final state interaction, located at $M_V=4.566\pm0.007$ GeV. Meanwhile, $X(4660)$ remains to be a typical Breit-Wigner resonance, and is hence of confinement nature. Our analysis strongly suggests the existence of the virtual pole with statistical significance of $4.2$ standard deviation ($σ$). Nevertheless, the conclusion crucially depends on the line-shape of cross sections which are of limited statistics, hence we urge new experimental analyses from Belle II, BESIII, and LHCb to settle the issue.

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arXiv2019

New Insights on Low Energy $πN$ Scattering Amplitudes: Comprehensive Analyses at $\mathcal{O}(p^3)$ Level

A production representation of partial-wave $S$ matrix is utilized to construct low-energy elastic pion-nucleon scattering amplitudes from cuts and poles on complex Riemann sheets. Among them, the contribution of left-hand cuts is estimated using the $\mathcal{O}(p^3)$ results obtained in covariant baryon chiral perturbation theory within the extended-on-nass-shell scheme. By fitting to data on partial-wave phase shifts, it is indicated that the existences of hidden poles in $S_{11}$ and $P_{11}$ channels, as conjectured in our previous paper~\citep{Wang:2017agd}, are firmly established. Specifically, the pole mass of the $S_{11}$ hidden resonance is determined to be $(895\pm81)-(164\pm23)i$ MeV, whereas, the virtual pole in the $P_{11}$ channel locates at $(966\pm18)$ MeV. It is found that analyses at the $\mathcal{O}(p^3)$ level improves significantly the fit quality, comparing with the previous $\mathcal{O}(p^2)$ one. Quantitative studies with cautious physical discussions are also conducted for the other $S$- and $P$-wave channels.

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arXiv2018

On the Existence of $N^*(890)$ Resonance in $S_{11}$ Channel of $πN$ Scatterings

Low-energy partial-wave $πN$ scattering data is reexamined with the help of the production representation of partial-wave $S$ matrix, where branch cuts and poles are thoroughly under consideration. The left-hand cut contribution to the phase shift is determined, with controlled systematic error estimates, by using the results of $\mathcal{O}(p^3)$ chiral perturbative amplitudes obtained in the extended-on-mass-shell scheme. In $S_{11}$ and $P_{11}$ channels, severe discrepancies are observed between the phase shift data and the sum of all known contributions. Statistically satisfactory fits to the data can only be achieved by adding extra poles in the two channels. We find that a $S_{11}$ resonance pole locates at $\sqrt{z_{r}}=(0.895\pm0.081)-(0.164\pm0.023)i$ GeV, on the complex $s$-plane. On the other hand, a $P_{11}$ virtual pole, as an accompanying partner of the nucleon bound-state pole, locates at $\sqrt{z_{v}}=(0.966\pm0.018)$ GeV, slightly above the nucleon pole on the real axis below threshold. Physical origin of the two newly established poles is explored to the best of our knowledge. It is emphasized that the $\mathcal{O}(p^3)$ calculation greatly improves the fit quality comparing with the previous $\mathcal{O}(p^2)$ one.

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arXiv2018

The pole structure of low energy $πN$ scattering amplitudes

This report presents an investigation of the pion-nucleon elastic scattering in low energy region using a production representation of the partial wave $S$ matrix. The phase shifts are separated into contributions from poles and branch cuts, where the left-hand cut term can be evaluated by tree-level covariant baryon chiral perturbation theory. A comparison between the sum of known contributions and the data in $S$- and $P$- wave channels is made. It is found that the known components in $S_{11}$ and $P_{11}$ channels are far from enough to saturate the corresponding experimental data, indicating the existence of low-lying hidden poles. The positions of those hidden poles are figured out and the physics behind them are explored.

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arXiv2018

New Insights on Low Energy $πN$ Scattering Amplitudes

The $S$- and $P$- wave phase shifts of low-energy pion-nucleon scatterings are analysed using Peking University representation, in which they are decomposed into various terms contributing either from poles or branch cuts. We estimate the left-hand cut contributions with the help of tree-level perturbative amplitudes derived in relativistic baryon chiral perturbation theory up to $\mathcal{O}(p^2)$. It is found that in $S_{11}$ and $P_{11}$ channels, contributions from known resonances and cuts are far from enough to saturate experimental phase shift data -- strongly indicating contributions from low lying poles undiscovered before, and we fully explore possible physics behind. On the other side, no serious disagreements are observed in the other channels.

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