arXiv subjects

Chao-Wei Shen

Publications and source records attributed to Chao-Wei Shen.

17 recordsLinked to original sources

arXiv2025

Towards the LHCb pentaquark modes in the single-charm sector

The mass spectrum of $Λ_c$ baryon family is investigated within the $DN$-$D^*N$ coupled-channel framework using two phenomenological approaches for the low-energy $D^{(*)} N$ interactions: the heavy quark effective theory and the flavor-symmetry-constrained effective Lagrangian method. It is shown that the LHCb pentaquark states have direct analogs in the $Λ_c$ family. Specifically, $Λ_c(2765)$, $Λ_c(2910)$, and $Λ_c(2940)$ mirror the patterns of $P_{c\bar{c}}(4312)$, $P_{c\bar{c}}(4440)$, and $P_{c\bar{c}}(4457)$, respectively. These mirror pentaquark modes offer valuable insights into the quantum numbers of the two heavy $P_{c\bar{c}}$ states, which remain experimentally undetermined. Further exploration of such correlations among exotic hadronic states across different flavor sectors will be crucial for developing a comprehensive theoretical understanding of the modern hadron spectrum.

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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 $J/ψp$ invariant mass distribution of the $Λ_b^0\to J/ψp K^-$ 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 $\bar{D}Σ_c$, $P_c(4380)\,3/2^-$ by $\bar{D}Σ_c^*$, while the $P_c(4440)\,1/2^-$ and $P_c(4457)\,3/2^-$ states both turn out as composite states of $\bar{D}^*Σ_c$. 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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arXiv2025

Box Singularity Conditions in Box Diagrams of Decay Processes

Since 1959, singularities within single-loop diagrams have been studied. They are believed to significantly influence our understanding of experimental observables. In this study, we explore the singularities that arise from box diagrams in the decay process, which can be classified into two distinct categories. A comprehensive analysis of box singularities has been conducted, wherein we have derived and presented specific conditional formulae to ascertain the occurrence of singularities, along with the related physical scenarios.

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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

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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arXiv2022

Light baryon resonances from a coupled-channel study including $\mathbf{KΣ}$ photoproduction

The Jülich-Bonn dynamical coupled-channel approach is extended to include $KΣ$ photoproduction off the proton. Differential cross section and (double) polarization data for $K^+Σ^0$ and $K^0Σ^+$ are analysed simultaneously with the pion- and photon-induced production of $πN$, $ηN$, $KΛ$, and $KΣ$ final states, totaling more than 67,000 data points for center-of-mass energies $W<2.4$ GeV. Based on the fit results the spectrum of $N^*$ and $Δ$ resonances is extracted in terms of pole positions and residues. We discuss the impact of the $γp\to KΣ$ channels in detail and investigate the influence of recent polarization data for $ηp$ photoproduction.

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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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arXiv2022

$P_{cc}^N$ states in a unitarized coupled-channel approach

Starting from an effective Lagrangian with heavy quark spin symmetry embedded, the coupled-channel dynamics of the doubly charmed systems $D^{(*)} Σ_c^{(*)}$ is investigated. The potential underlying our investigation includes $t$-channel pseudoscalar and vector meson exchanges. A series of $S$-wave bound states with isospin $I=1/2$ is found by applying the first iterated solution of the $N/D$ method: one state with binding energy $23$ MeV in the $5/2^-$ $D^*Σ_c^*$ channel, three states with binding energy $26$, $30$ and $7$ MeV (relative to the thresholds from low to high, respectively) in the $3/2^-$ $DΣ_c^*$-$D^*Σ_c$-$D^*Σ_c^*$ system and three states with binding energy $32$, $8$ and $16$ MeV in the $1/2^-$ $DΣ_c$-$D^*Σ_c$-$D^*Σ_c^*$ system. Those $P_{cc}^N$ states serve as the open-charm partners of the hidden charm pentaquarks $P_ψ^N$ observed by the LHCb Collaboration.

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arXiv2022

Resonances in heavy meson - heavy baryon coupled-channel interactions

The interactions of $\bar{D}^{(*)} Λ_c - \bar{D}^{(*)}Σ_c^{(*)}$ are studied within the framework of a dynamical coupled-channel approach. A series of bound states and resonances with different spin and parity are dynamically generated in the hidden charm sector. Four $S$-wave bound states are found in the mass range of 4.3 to 4.5 GeV, close to the pentaquark states observed by LHCb. Two of the states have a spin parity of $J^P= 1/2^-$ and the other two have $J^P=3/2^-$. In addition, several resonances with different spin and parity in higher partial waves are predicted.

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arXiv2022

Prediction of five-flavored pentaquarks

We analyze the possibility of the existence of a fully exotic pentaquark state $udsc\bar{b}$, which is made from the five different flavors participarting in the strong interactions. We investigate the coupled channel effects of the $B^{(*)} Ξ_c-B^{(*)} Ξ_c^\prime$ system through $t$-channel vector meson exchange to search for such states. A $B Ξ_c$ and a $B Ξ_c^\prime$ bound state are found to have binding energies of about $10-30$~MeV with $B_sΛ_c$ and $B_cΛ$ being the possible decay channels. Similarly, a bound state is formed in the $B^* Ξ_c$ and $B^* Ξ_c^\prime$ channels, respectively. These states could be searched for through the $pp\to B_cΛX$ or $pp\to B_s^{(*)}Λ_c X$ processes by the LHCb collaboration.

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arXiv2021

Detecting the pure triangle sigularity effect through the $ψ(2S) \to p \bar{p} η/ p \bar{p} π^0$ process

In this work, the triangle singularity mechanism is investigated in the $ψ(2S) \to p \bar{p} η/ p \bar{p} π^0$ process. The triangle loop composed by $J/ψ$, $η$ and $p$ has a singularity in the physical kinematic range for the $ψ(2S) \to p \bar{p} η/ p \bar{p} π^0$ process, and it would generate a very narrow peak in the invariant mass spectrum of $pη(π)$ around $1.56387$ GeV, which is far away from both the threshold and relative resonances. In these processes, all the involved vertices are constrained by the experimental data. Thus, we can make a precise model independent prediction here. It turns out that the peak in the $pη$ invariant mass spectrum is visible, while it is very small in the $pπ^0$ invariant mass spectrum. We expect this effect shown in $p \bar{p} η$ final state can be observed by the Beijing Spectrometer (BESIII) and Super Tau-Charm Facility (STCF) in the future.

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arXiv2021

Graphic Method for Arbitrary $n$-body Phase Space

In quantum field theory, the phase space integration is an essential part in all theoretical calculations of cross sections and decay widths. It is also needed for computing the imaginary part of a physical amplitude. A key problem is to get the phase space formula expressed in terms of any chosen invariant masses in an $n$-body system. We propose a graphic method to quickly get the phase space formula of any given invariant masses intuitively for an arbitrary $n$-body system in general $D$-dimensional spacetime, with the involved momenta in any reference frame. The method also greatly simplifies the phase space calculation just as what Feynman diagrams do in calculating scattering amplitudes.

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arXiv2020

Exploring possible triangle singularities in the $Ξ^-_{b} \to K^- J/ψΛ$ decay

We analyze possible singularities in the $J/ψΛ$ invariant mass distribution of the $Ξ^-_{b}~\to~K^- J/ψΛ$ process via triangle loop diagrams. Triangle singularities in the physical region are found in 18 different triangle loop diagrams. Among those with $Ξ^*$-charmonium-$Λ$ intermediate states, the one from the $χ_{c1} Ξ(2120) Λ$ loop, which is located around 4628 MeV, is found the most likely to cause observable effects. One needs $S$- and $P$-waves in $χ_{c1} Λ$ and $J/ψΛ$ systems, respectively, when the quantum numbers of these systems are $1/2^+$ or $3/2^+$. When the quantum numbers of the $Ξ(2120)$ are $J^P=1/2^+$, $1/2^-$ or $3/2^+$, the peak structure should be sharper than the other $J^P$ choices. This suggests that although the whole strength is unknown, we should pay attention to the contributions from the $Ξ^*$-charmonium-$Λ$ triangle diagram if structures are observed in the $J/ψΛ$ invariant mass spectrum experimentally. In addition, a few triangle diagrams with the $D_{s1}^*(2700)$ as one of the intermediate particles can also produce singularities in the $J/ψΛ$ distribution, but at higher energies above 4.9 GeV.

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arXiv2019

Decay behaviors of possible $Λ_{c\bar{c}}$ states in hadronic molecule pictures

In 2010, $Λ^*_{c\bar{c}}$ states were predicted as the strange number $S=-1$ partners of $N^*_{c\bar{c}}$, which are well known now as the $P_c$ states and observed experimentally by LHCb Collaboration. We analyze the decay behaviors of $Λ_{c\bar{c}}$ as S-wave hadronic molecules within the effective Lagrangian framework by a similar method, which has been applied on $P_c$ states successfully. With partial widths of possible decay channels calculated, we find that $Λ_{c\bar{c}}(4213)$ and $Λ_{c\bar{c}}(4403)$, which are formed as pseudoscalar meson baryon molecules, mainly decay to the $η_c Λ$ channel. For the two vector meson baryon molecule states, our results show that the total decay width with $J^P=\frac12^-$ is by one order of magnitude larger than that with $J^P=\frac32^-$. The decay patterns and relative decay ratios are very different for $Λ_{c\bar{c}}(4370)$ being a $D_s^{* -} Λ_c^+$ or $\bar{D}^{*} Ξ_c$ molecule state. The main decay channels of $Λ_{c\bar{c}}(4550)$ are $\bar{D}^{(*)} Ξ^{(*,\prime)}_c$ because of the pseudoscalar meson exchange mechanism. In addition, $\bar{D}^{*} Ξ_c$ is the dominant decay channel of $Λ_{c\bar{c}}(4490)$ which is assumed as a $\bar{D} Ξ_c^{*}$ bound state. These decay patterns of the $Λ^*_{c\bar{c}}$ states would provide a guidance for their future experimental searches and help us to understand their internal structures.

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arXiv2018

Decay behavior of the strange and beauty partners of $P_c$ hadronic molecules

We extend our previous study on the decay behavior of $P_c$ hadronic molecules to their strange and beauty partners. While $P_c(4380)$ and $P_c(4450)$ locate just below the $\bar DΣ_c^*$ and $\bar D^*Σ_c$ thresholds, respectively, their proposed strange partners $N(1875)$ and $N(2080)$ sit just below the $KΣ^*$ and $K^*Σ$ thresholds, respectively. Using the effective Lagrangian approach as the same as for the study of $P_c$ hadronic molecular states and with the couplings determined by the $\mathrm{SU}(3)$ flavor symmetry, the decay patterns of $N(1875)$ and $N(2080)$ are obtained assuming them to be the $S$-wave $KΣ^*$ and $K^*Σ$ molecules, respectively. It is found that the measured decay properties of $N(1875)$ and $N(2080)$ are reproduced well. Our results suggest that both $N(1875)$ and $N(2080)$ can be ascribed as the hadronic molecular pentaquark states in the hidden strangeness sector with quantum number $I(J^P)=1/2({3/2}^-)$. Further checks on their hadronic molecule nature by various experiments are proposed. With the same approach, we also give our predictions for the decay behavior of the possible beauty partners of the $P_c$ hadronic molecular states. The $B^*Λ_b$ is found to be the largest decay mode for both $BΣ_b^*$ and $B^*Σ_b$ hadronic molecules, hence can be used to look for the hidden beauty pentaquark states in forthcoming experiments.

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arXiv2018

Exploratory study of possible resonances in the heavy meson - heavy baryon coupled-channel interactions

We use a unitary coupled-channel model to study the $\bar{D} Λ_c - \bar{D} Σ_c$ interactions. In our calculation, SU(3) flavor symmetry is applied to determine the coupling constants. Several resonant and bound states with different spin and parity are dynamically generated in the mass range of the recently observed pentaquarks. The approach is also extended to the hidden beauty sector to study the $B Λ_b - B Σ_b$ interactions. As the $b$-quark mass is heavier than the $c$-quark mass, there are more resonances observed for $B Λ_b - B Σ_b$ interactions and they are more tightly bound.

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arXiv2016

Disentangling the hadronic molecule nature of the $P_c(4380)$ pentaquark-like structure

We demonstrate that the relative ratio of the decays of hidden charm pentaquark-like structure $P^+_c(4380)$ to $\bar{D}^* Λ_c^+$ and $J/ψp$ are very different for $P^+_c$ being $\bar{D} Σ_c^*(2520)$ or $\bar{D}^* Σ_c(2455)$ molecule states. While the partial width of the $\bar{D} Σ_c^*(2520)$ molecule to the $\bar{D}^* Λ_c^+$ is much larger, by one order of magnitude, than that to the $J/ψp$, the $\bar{D}^* Σ_c(2455)$ molecule shows a different pattern. Our analysis shows that the $\bar{D} Σ_c^*$ bound state ansatz is more reasonable than the $\bar{D}^* Σ_c$ one to explain the broad $P_c(4380)$ structure. We suggest to search for the $P_c(4380)$ in the $\bar{D}^* Λ_c^+$ system, which can be used to disentangle the nature of the $P^+_c(4380)$ structure.

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