arXiv subjects

Youchang Yang

Publications and source records attributed to Youchang Yang.

13 recordsLinked to original sources

arXiv2025

Exploring the nature of $\eta_{1}(1855)$ and it's partner in a chiral quark model

Inspired by the recent experimental discoveries of $X(3872)$ ($c\bar{q}$-$q\bar{c}$) and $T_{cc}$ ($c\bar{q}$-$c\bar{q}$), we systematically study two four-quark systems: the $K K_1$ ($q\bar{s}$-$q\bar{s}$) system and the $K \bar{K}_1$ ($q\bar{s}$-$s\bar{q}$) system, which is a candidate for the recently observed $\eta_1(1855)$. Within the framework of an accurate few-body calculation method (GEM), we employ the chiral quark model to simultaneously consider the molecular and diquark structures of these two multiquark systems and include their channel coupling effects. Our results show that the $K \bar{K}_1$ system remains a scattering state. On the other hand, due to the presence of a good-diquark structure in the $K K_1$ system, we obtain a bound state in the coupled-channel calculation. The primary contribution to the binding energy comes from the exchange of $\pi$-meson and $\sigma$-meson. The inter-quark distance indicates that it is a compact four-quark structure.

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arXiv2025

Investigating the nature of $N(1535)$ and $\Lambda(1405)$ in a quenched chiral quark model

In this work, we systematically study $N(1440)$, $N(1535)$, and $\Lambda(1405)$ in both the quenched three-quark and five-quark frameworks using the Gaussian Expansion Method (GEM) within the chiral quark model. Our calculations show that $N(1535)$ can be reproduced as a three-quark state ($N(1P)$), while $N(1440)$ and $\Lambda(1405)$ cannot be accommodated as the three-quark candidates, ($N(2S)$ and $\Lambda(1P)$), respectively. In the five-quark framework, we find that the $\Lambda K$ state for $N(1535)$ can not form a bound state, while in the $N\bar{K}$ channel there will $\Lambda(1405)$ form a shallow bound state. Based on the complex-scaling method, we performed complete coupled-channels calculations and obtained six resonance states with energies ranging from 1.8 GeV to 2.2 GeV, in addition with one bound state located around $\Sigma \pi$ channel. However, neither molecular candidates in $\Lambda K$ channel for $N(1535)$ nor $N\bar{K}$ for $\Lambda(1405)$ are included in these states. This is because the strong coupling between $N\bar{K}$ and $\Sigma \pi$ will make the $N\bar{K}$ unbound, while the weak coupling between $\Lambda K$ and $\Sigma K$ can not help form a stable structure around $\Lambda K$ threshold. Thus, under the quenched quark model, our results support $N(1535)$ as a three-quark state, while $N(1440)$ is neither a three-quark nor a five-quark state. In addition, we find that although $\Lambda(1405)$ can be primarily a five-quark state, it requires a mixture of three-quark and five-quark components for stability. In the future, an exploration on the mixing effects between bare baryons with these relevant two-body hadronic channel components will be carried out to further test our conclusions.

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arXiv2024

Investigating the $p$-$\Omega$ Interaction and Correlation Functions

Motivated by experimental measurements, we investigate the $p$-$\Omega$ correlation functions and interactions on the basis of a quark model. By solving the inverse scattering problem with channel coupling, we renormalize the coupling to other channels into an effective single-channel $p$-$\Omega$ potentials. The effects of Coulomb interaction and spin-averaging are also discussed. According to our results, the depletion of the $p$-$\Omega$ correlation functions, which is attributed to the $J^P = 2^+$ bound state not observed in the ALICE Collaboration's measurements [Nature \textbf{588}, 232 (2020)], can be explained by the contribution of the attractive $J^P = 1^+$ component in spin-averaging. So far, we have provided a consistent description of the $p$-$\Omega$ system from the perspective of the quark model, including the energy spectrum, scattering phase shifts, and correlation functions. The existence of the $p$-$\Omega$ bound state has been supported by all three aspects. Additionally, a sign of the $p$-$\Omega$ correlation function's subtle sub-unity part can be seen in experimental measurements, which warrants more precise verification in the future.

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arXiv2024

Dynamical study of $D^{}DK$ and $D^{}D \bar{D}$ systems at quark level

Inspired by that Belle\uppercase\expandafter{\romannumeral2} Collaboration recently reported $T_{cc}$, which can be interpreted as a molecular $DD^{*}$, we investigated the trihadron system of $T_{cc}$ partner with $IJ^{P}$=$01^{-}$ in the framework of a chiral quark model. It's widely accepted that the main component of $X(3872)$ contains the molecular $\bar{D}D^{*}$, while the main component of $D_{s0}^{*}(2317)$ is molecular $DK$. Based on these three well-known exotic states, $T_{cc} (DD^{*})$, $X(3872) (\bar{D}D^{*})$ and $D_{s0}^{*}(2317) (DK)$, we dynamically investigate $D^{*}DK$ and $DD^{*}\bar{D}$ systems at quark level to search for possible bound states. The results show that both of them are bound states, in which the binding energy of the molecular state $DD^*K$ is relatively small, only 0.8 MeV, while the binding energy of $DD^*\bar{D}$ is up to 1.9 MeV. According to the calculation results of the Root-square-mean distances, the spatial structure of the two systems shows obvious ($DD^*$)-($\bar{D}$/$K$) structure, in which $D$ is close to $D^*$ while $DD^*$ as a whole is relatively distant from the third hadron ($\bar{D}$/$K$), which are similar to the nucleon-electron structure. As a result, we strongly recommend that these bound states $DD^*\bar{D}$ and $DD^*K$ are searched for experimentally.

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arXiv2023

Charmonium mass shifts in an unquenched quark model

In this paper, we performed a coupled-channel calculation and evaluated the mass shifts for all $1S$, $2S$, $1P$, $2P$ and $1D$ charmonium valence states below 4 GeV, by incorporating the four-quark components ($D$, $D^*$, $D_s$ and $D_s^*$ meson pairs) into the quark model. The valence-continuum coupling is provided by the $^3P_0$ quark-pair creation model. The induced mass shifts appear to be large and negative with the original transition operator in $^3P_0$ model, which raised up challenges for the valence quark model. More QCD-motivated models should be employed for the quark-pair creation Hamiltonian. So herein, we recalculated the mass shifts with the improved $^3P_0$ transition operator introduced in our previous work and the mass shifts are reduced by $75\%$ averagely. Besides, as a exercise, we adjust the confinement parameter $Δ$ and recalculate the spectrum of the charmonium states. The masses of some charmonium states are reproduced well.

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arXiv2022

Molecular state interpretation of charmed baryons in the quark model

Stimulated by the observation of $Λ_c(2910)^+$ by the Belle Collaboration, the $S$-wave $qqq\bar{q}c~(q=u~\text{or}~d)$ pentaquark systems with $I$ = 0, $J^P$ = $\frac{1}{2}^-,~\frac{3}{2}^- and~\frac{5}{2}^-$ are investigated in the framework of quark delocalization color screening model(QDCSM). The real-scaling method is utilized to check the bound states and the genuine resonance states. The root mean square of cluster spacing is also calculated to study the structure of the states and estimate if the state is resonance state or not. The numerical results show that $Λ_{c}(2910)$ cannot be interpreted as a molecular state, and $Σ_{c}(2800)$ cannot be explained as the $ND$ molecular state with $J^P=1/2^-$. $Λ_{c}(2595)$ can be interpreted as the molecular state with $J^P=\frac{1}{2}^-$ and the main component is $Σ_{c}π$. $Λ_{c}(2625)$ can be interpreted as the molecular state with $J^P=\frac{3}{2}^-$ and the main component is $Σ_{c}^{*}π$. $Λ_{c}(2940)$ is likely to be interpreted as a molecular state with $J^P=3/2^-$, and the main component is $ND^{*}$. Besides, two new molecular states are predicted, one is the $J^P=3/2^-$ $Σ_{c}ρ$ resonance state with the mass around 3140 MeV, another one is the $J^P=\frac{5}{2}^-$ $Σ_{c}^*ρ$ with the mass of 3188.3 MeV.

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arXiv2022

Double-heavy tetraquarks with strangeness in the chiral quark model

Recently, some progresses have been made on the double-heavy tetraquarks in the experiments, such as $T_{cc}$ reported by LHCb Collaboration, and $X_{cc\bar{s}\bar{s}}$ reported by the Belle Collaboration. Coming on the heels of our previous work about $T_{cc}$ and $T_{bb}$, we present a study on the bound states and the resonant states of its companions $QQ\bar{q}\bar{s}$ ($Q=c,b; q=u, s$) tetraquarks with strange flavor in the chiral quark model. Two pictures, one with meson-meson picture, another with diquark-antidiquark picture and their couplings are considered in our calculations. Isospin violation is neglected herein. Our numerical analysis indicates that only the state $bb\bar{u}\bar{s}$ with $\frac{1}{2}(1^+)$ is bound, with the binding energy 3.5 MeV. Besides, we also find some resonant states for the double-heavy strange tetraquarks with the real scaling method.

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arXiv2022

Investigation of the bottom analog of the Zcs(3985) state

Motivated by the recent discovery of the hidden charm exotic state with strangeness by the BESIII and LHCb Collaborations, we study the $S$ wave strange hidden bottom tetraquark in two kinds of quark models. Both meson-meson and diquark-antidiquark configurations are taken into account. The numerical results indicate that there is no bound state in both quark models. However, several resonance states have been predicted. Three resonance states with $I(J^{P})=\frac{1}{2}(0^{+})$ are found, the energy ranges of which are $10479\sim 10550$, $10528\sim 10632$, and $10597\sim 10681$ MeV, respectively. Three resonance states with $I(J^{P})=\frac{1}{2}(1^{+})$ are predicted to be located in $10491\sim 10675$, $10502\sim 10679$, and $10522\sim 10723$ MeV, respectively. Moreover, there also exist a resonance with $I(J^{P})=\frac{1}{2}(2^{+})$ and the mass is estimated to be $10531\sim 10680$ MeV. All these predicted states in the present work should be accessible for the further experiments in LHCb

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arXiv2021

Systematic study of $D_{s0}^{*}$(2317) in quark models

Recently, the BES\uppercase\expandafter{\romannumeral3} Collaboration updated the data for the exotic state, $D^{*}_{s0}(2317)$, with a mass of $2318.3\pm1.2\pm1.2$ MeV from the positronium annihilation process. Inspired by the experiment, we systematically investigated the $c\bar{q}$ meson family spectrum from the perspectives of two-quark, four-quark, and mixed two-four-quark structures, including $D_s$, $D_s^{*}$, $D_{s0}^{*}(2317)$, and $D_{s1}(2460)$, with the help of the Gaussian expansion method, which is a very accurate calculation method for few-body systems. We found that with appropriate spin-orbit coupling parameter $a_s$, the chiral quark model can effectively describe both $D_{s0}^{*}(2317)$ and $D_{s1}(2460)$. The four-quark calculation shows that the $DK$ state does not form a bound state, but the effective potential calculation shows an attractive interaction between them. Finally, we performed mixed two-four-quark calculations, and the results, with the help of the unquenched effect, show that the energies of $D_{s0}^{*}(2317)$ and $D_{s1}(2460)$ are in better agreement with experimental values. Therefore, we conclude that these two particles are good candidates for mixed two-four-quark states.

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arXiv2013

Baryonia and near-threshold enhancements

The baryon-antibaryon spectrum consisting of strange, charm and bottom quarks is studied in the color flux-tube model with a multi-body confinement interaction. Numerical results indicate that many low-spin baryon-antibaryon states can form compact hexaquark states and are stable against the decay into a baryon and an antibaryon. The multi-body confinement interaction as a binding mechanism plays an important role in the formation of the states. They can be searched in the $e^+e^-$ annihilation and charmonium or bottomonium decay if they really exist. The newly reported states, X(1835), X(2370), Y(2175), Y(4360) and Y_b(10890), may be interpreted as $N\bar{N}$, $Δ\barΔ$, $Λ\barΛ$, $Λ_c\barΛ_c$ and $Λ_b\barΛ_b$ states, respectively.

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arXiv2012

X(1835), X(2120) and X(2370) in a flux tube model

Nonstrange baryonium spectrum is systematically studied by using the Gaussian expansion method in a flux tube model with the six-body confinement potential. All the model parameters are fixed by baryon properties, so the baryonium calculation is parameter-free. We find that X(1835) and X(2370), which are observed in the radiative decay of $J/ψ$ by BES collaboration, can be described as $N_8\bar{N}_8$ and $Δ_8\barΔ_8$ bound states with quantum numbers $I^GJ^{PC}=0^+0^{-+}$, respectively, such bound states should be color confinement resonances with three-dimensional configurations similar to dumbbell, however, X(2120) can not be accommodated in our model.

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arXiv2012

Possible interpretation of the $Z_b$(10610) and $Z_b$(10650) in a chiral quark model

Motivated by the two charged bottomonium-like resonances $Z_b$(10610) and $Z_b$(10650) newly observed by the Belle collaboration, the possible molecular states composed of a pair of heavy mesons, $B\bar{B}, B\bar{B}^*, B^*\bar{B}^*, B_s\bar{B}$, etc (in S-wave), are investigated in the framework of chiral quark models by the Gaussian expansion method. The bound states $B\bar{B}^*$ and $B^*\bar{B}^*$ with quantum numbers $I(J^{PC})=1(1^{+-})$, which are good candidates for the $Z_b(10610)$ and $Z_b(10650)$ respectively, are obtained. Other three bound states $B\bar{B}^*$ with $I(J^{PC})=0(1^{++})$, $B^*\bar{B}^*$ with $I(J^{PC})=1(0^{++}), 0(2^{++})$ are predicted. These states may be observed in open-bottom or hidden-bottom decay channel of highly excited $Υ$. When extending directly the quark model to the hidden color channel of the multi-quark system, more deeply bound states are found. Future experimental search of those states will cast doubt on the validity of applying the chiral constituent quark model to the hidden color channel directly.

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arXiv2010

Dynamical study of the $X$(3915) as a molecular $D^\bar{D^}$ state in a quark model

Considering the coupling of color $1 \otimes 1$ and $8 \otimes 8$ structures, we calculate the energy of the newly observed $X$(3915) as $S-$wave $D^*\bar{D^*}$ state in the Bhaduri, Cohler, and Nogami quark model by the Gaussian Expansion Method. Due to the color coupling, the bound state of $D^*\bar{D^*}$ with $J^{PC}=0^{++}$ is found, which is well consonant with the experimental data of the $X$(3915). The bound state of $B^*\bar{B^*}$ with $J^{PC}=0^{++}$ and $2^{++}$ are also predicted in this work.

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