arXiv subjects

Bing-Song Zou

Publications and source records attributed to Bing-Song Zou.

At least 55 records · Page 3Linked to original sources

arXiv2023

Ground states of all mesons and baryons in a quark model with Hidden Local Symmetry

We extend the chiral quark model for $u$, $d$, $c$ and $b$ quarks with vector mesons, which we proposed in the previous analysis, to a model with the $s$ quark. We include the nonet pseudo-scalar and vector mesons together with the singlet scalar meson based on the SU(3)$_L \times$SU(3)$_R$ chiral symmetry combined with the Hidden Local Symmetry, which mediate force among $u$, $d$ and $s$ quarks. We fit the model parameters to the known ground state mesons and baryons. We show that the mass spectra of those hadrons are beautifully reproduced. We predict the masses of missing ground states, one meson and twenty baryons, which will be tested in the future experiment.

hep-ph↗

arXiv2023

Quark model with Hidden Local Symmetry and its application to $T_{cc}$

We propose a chiral quark model including the $ω$ and $ρ$ meson contributions in addition to the $π$ and $σ$ meson contributions. We show that the masses of the ground state baryons such as the nucleon, $Λ_c$ and $Λ_b$ are dramatically improved in the model with the vector mesons compared with the one without them. The study of the tetraquark $T_{cc}$ is also performed in a coupled channel calculation and the resultant mass is much closer to its experimental value than the result without vector meson contribution. This approach can be applied to the future study of multi-quark systems.

hep-ph↗

arXiv2023

Strange molecular partners of $P_c$ states in $γp\toϕp$ reaction

Based on the high statistical data of the CLAS Collaboration on $γp \to ϕp$ reaction in the center-of-mass energy range of 2.2 GeV to 2.8 GeV, we investigate the possible existence of strange molecular partners of $P_c$ states, i.e., $N^*(2080)$ and $N^*(2270)$ as $K^*Σ$ and $K^*Σ^*$ molecular states. In addition to the t-channel Pomeron exchange, t-channel meson exchange including pseudo-scalar meson $(π,η)$, scalar meson $(σ, a_0(980), f_0(980))$, axial-vector meson $f_1(1285)$, tensor meson $f_2(1270)$, as well as s- and u-channel proton exchange, including s-channel $N^*(2080)$ and $N^*(2270)$ states can fit the data very well. The fitted coupling constants of these $N^*$ molecular states to $pϕ$ and $γp$ are consistent with the results directly calculated from the relevant hadronic triangle diagrams of the molecular picture.

hep-ph↗

arXiv2023

Understanding the $0^{++}$ and $2^{++}$ charmonium(-like) states near 3.9 GeV

We propose that the $X(3915)$ observed in the $J/ψ\,ω$ channel is the same state as the $χ_{c2}(3930)$, and the $X(3960)$, observed in the $D_s^+D_s^-$ channel, is an $S$-wave $D_s^+ D_s^-$ hadronic molecule. In addition, the $J^{PC}=0^{++}$ {component in the $B^+\to D^+D^-K^+$} assigned to the $X(3915)$ in the current {\it Review of Particle Physics} has the same origin as the $X(3960)$, which has a mass around 3.94~GeV. To check the proposal, the available data in the $D\bar D$ and $D_s^+ D_s^-$ channels from both $ B$ decays and $γγ$ fusion reaction are analyzed considering both the $D\bar D$-$D_s\bar D_s$-$D^*\bar D^*$-$D_s^*\bar D_s^*$ coupled channels with $0^{++}$ and a $2^{++}$ state introduced additionally. It is found that all the data in different processes can be simultaneously well reproduced, and the coupled-channel dynamics produce four hidden-charm scalar molecular states with masses around 3.73, 3.94, 3.99 and 4.23~GeV, respectively. The results may deepen our understanding of the spectrum of charmonia as well as of the interactions between charmed hadrons.

hep-ph↗

arXiv2023

On the $η_1(1855)$, $π_1(1400)$ and $π_1(1600)$ as dynamically generated states and their SU(3) partners

In this work, we interpret the newly observed $η_1(1855)$ resonance with exotic $J^{PC}=1^{-+}$ quantum numbers in the $I=0$ sector, reported by the BESIII Collaboration, as a dynamically generated state from the interaction between the lightest pseudoscalar mesons and axial-vector mesons. The interaction is derived from the lowest order chiral Lagrangian from which the Weinberg-Tomozawa term is obtained, describing the transition amplitudes among the relevant channels, which are then unitarized using the Bethe-Salpeter equation, according to the chiral unitary approach. We evaluate the $η_1(1855)$ decays into the $ηη^{\prime}$ and $K\bar{K}^*π$ channels and find that the latter has a larger branching fraction. We also investigate its SU(3) partners, and according to our findings, the $π_1(1400)$ and $π_1(1600)$ structures may correspond to dynamically generated states, with the former one coupled mostly to the $b_1π$ component and the latter one coupled to the $K_1(1270)\bar{K}$ channel. In particular, our result for the ratio $Γ(π_1(1600)\to f_1(1285)π)/ Γ(π_1(1600)\to η^{\prime}π)$ is consistent with the measured value, which supports our interpretation for the higher $π_1$ state. We also report two poles with a mass about 1.7~GeV in the $I=1/2$ sector, which may be responsible for the $K^*(1680)$. We suggest searching for two additional $η_1$ exotic mesons with masses around 1.4 and 1.7~GeV. In particular, the predicted $η_1(1700)$ is expected to have a width around 0.1~GeV and can decay easily into $K\bar Kππ$.

hep-ph↗

arXiv2023

A new look at the $P_{cs}$ states from a molecular perspective

We have a look at the $P_{cs}$ states generated from the interaction of $\bar D^{(*)} Ξ^{(\prime*)}_c$ coupled channels. We consider the blocks of pseudoscalar-baryon $({\frac12}^+, {\frac32}^+)$ and vector-baryon $({\frac12}^+, {\frac32}^+)$, and find $10$ resonant states coupling mostly to $\bar D Ξ_c, \bar D^* Ξ_c,\bar D Ξ'_c, \bar D^* Ξ'_c,\bar D Ξ^*_c$ and $\bar D^* Ξ^*_c$. A novel aspect of the work is the realization that the $\bar D Ξ_c,\bar D_sΛ_c$ or $\bar D^* Ξ_c,\bar D^*_sΛ_c$ channels, with a strong transition potential, collaborate to produce a larger attraction than the corresponding states $\bar D Σ_c,\bar DΛ_c$ or $\bar D^* Σ_c,\bar D^*Λ_c$ appearing in the generation of the strangenessless $P_{c}$ states, since in the latter case the transition potential between those channels is zero. The extra attraction obtained in the $\bar D Ξ_c,\bar D^* Ξ_c$ pairs preclude the association of these channels to the $P_{cs}(4338)$ and $P_{cs}(4459)$ states respectively. Then we find a natural association of the $P_{cs}(4338)$ state coupling mostly to $\bar D^* Ξ_c$ while the $P_{cs}(4459)$ is associated to the state found that couples mostly to $\bar D Ξ'_c$. Four more states appear, like in other molecular pictures, and some of the states are degenerate in spin. Counting different spin states we find $10$ states, which we hope can be observed in the near future.

hep-ph↗

arXiv2022

Coupled Channel Effects for the Charmed-Strange Mesons

We make a systematic calculation of the spectra and hadronic decays of the $D_s$ system in a coupled channel framework, where the unquenched effects are induced by the $^3P_0$ model. In the calculation, the wave functions are obtained by using a nonrelativistic potential model and are handled precisely with Gaussian Expansion Method. Even though the fitting mainly focuses on the spectrum, our model agrees well with the experiments on both the spectra and the hadronic decays, suggesting that the coupled channel effect could result in a reasonable and coherent description of the $D_s$ mesons. Based on the calculation, we give a detailed analysis on various aspects of the excited states, especially $D_s(2317), D_s(2460), D_s(2536), D_s(2860), D_s(3040)$. We also predict that $D_s(2{}^3P_0)$ should be a $D^*K^*$ dominant molecule with mass $2894$~MeV, which is only $5$~MeV below the $D^*K^*$ threshold.

hep-ph↗

arXiv2022

Prediction of a narrow exotic hadronic state with quantum numbers $J^{PC}=0^{--}$

Lots of charmonium-like structures have been observed in the last two decades. Most of them have quantum numbers that can be formed by a pair of charm and anticharm quarks, thus it is difficult to unambiguously identify the exotic ones among them. In this Letter, by exploiting heavy quark spin symmetry, we present a robust prediction of the hadronic molecular scenario, where the $ψ(4230),ψ(4360)$ and $ψ(4415)$ are identified as $D\bar D_1,D^*\bar D_1$ and $D^*\bar D^*_2$ bound states, respectively. We show that a flavor-neutral charmonium-like exotic state with quantum numbers $J^{PC}=0^{--}$, denoted as $ψ_0(4360)$, should exist as a $D^*\bar D_1$ bound state. The mass and width of the $ψ_0(4360)$} are predicted to be $(4366\pm18)$ MeV and less than 10 MeV, respectively. The $ψ_0(4360)$ is significant in two folds: no $0^{--}$ hadron has been observed so far, and a study of this state will enlighten the understanding of the mysterious vector mesons between 4.2 and 4.5 GeV, as well as the nature of previously observed exotic $Z_c$ and $P_c$ states. We propose that such an exotic state can be searched for in $e^+e^-\to ηψ_0(4360)$ and uniquely identified by measuring the angular distribution of the outgoing $η$ meson.

hep-ph↗

arXiv2022

Anticharmed strange pentaquarks from the one-boson-exchange model

Inspired by the LHCb's discovery of hidden-charm pentaquarks, the anticharmed strange pentaquarks $P_{\bar c s}$ in a favor of the hadronic molecule picture are investigated from the one-boson-exchange model. Similar to the hidden-charm pentaquarks, three molecular bound states, one with spin parity $J^P=1/2^-$ below the $\bar DΣ$ threshold and another two with $J^P=\{1/2^-,3/2^-\}$ below the $\bar D^*Σ$ threshold, are predicted at $3-3.2$ GeV mass region. The mass ordering of the later two states can be interchanged by different reductions of the $δ(r)$ term. Furthermore, resonances associated with these three bound states are examined by considering $ D_s^-N-\bar DΛ-\bar D Σ-\bar D^*Λ-\bar D^*Σ$ coupled-channel dynamics, and decay widths of them are predicted. Our study indicates that the $ D_s^- p$ invariant mass spectrum in the $\bar B_s^0\to \bar n D_s^- p$ decay is an appropriate place to detect the $P_{\bar c s}$ pentaquarks.

hep-ph↗

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.

hep-ph↗

arXiv2022

Hadronic molecules

A large number of experimental discoveries especially in the heavy quarkonium sector that did not at all fit to the expectations of the until then very successful quark model led to a renaissance of hadron spectroscopy. Among various explanations of the internal structure of these excitations, hadronic molecules, being analogues of light nuclei, play a unique role since for those predictions can be made with controlled uncertainty. We review experimental evidences of various candidates of hadronic molecules, and methods of identifying such structures. Nonrelativistic effective field theories are the suitable framework for studying hadronic molecules, and are discussed in both the continuum and finite volumes. Also pertinent lattice QCD results are presented. Further, we discuss the production mechanisms and decays of hadronic molecules, and comment on the reliability of certain assertions often made in the literature.

hep-ph↗

arXiv2022

Substructure of Multiquark Hadrons (Snowmass 2021 White Paper)

In recent years there has been a rapidly growing body of experimental evidence for existence of exotic, multiquark hadrons, i.e. mesons which contain additional quarks, beyond the usual quark-antiquark pair and baryons which consist of more than three quarks. In all cases with robust evidence they contain at least one heavy quark Q=c or b, the majority including two heavy quarks. Two key theoretical questions have been triggered by these discoveries: (a) how are quarks organized inside these multiquark states -- as compact objects with all quarks within one confinement volume, interacting via color forces, perhaps with an important role played by diquarks, or as deuteron-like hadronic molecules, bound by light-meson exchange? (b) what other multiquark states should we expect? The two questions are tightly intertwined. Each of the interpretations provides a natural explanation of parts of the data, but neither explains all of the data. It is quite possible that both kinds of structures appear in Nature. It may also be the case that certain states are superpositions of the compact and molecular configurations. This Whitepaper brings together contributions from many leading practitioners in the field, representing a wide spectrum of theoretical interpretations. We discuss the importance of future experimental and phenomenological work, which will lead to better understandingof multiquark phenomena in QCD.

hep-ph↗

arXiv2022

Interpretation of the $η_1(1855)$ as a $K\bar K_1(1400)+$ c.c. molecule

An exotic state with $J^{PC}=1^{-+}$, denoted by $η_1(1855)$, was observed by BESIII collaboration recently in $J/ψ\to γηη'$. The fact that its mass is just below the threshold of $K\bar K_1(1400)$ stimulates us to investigate whether this exotic state can be interpreted as a $K\bar K_1(1400)+$ c.c { molecule or not}. Using the one boson exchange model, we show that it is possible for $K\bar K_1(1400)$ with $J^{PC}=1^{-+}$ to bind together by taking the momentum cutoff $Λ\gtrsim 2$ GeV and yield the same binding energy as the experimental value when $Λ\approx 2.5$ GeV. In this molecular picture, the predicted branch ratio $\mathrm{Br}(η_1(1855)\toηη') \approx 15\%$ is consistent with the experimental results, which again supports the molecular explanation of $η_1(1855)$. Relevant systems, namely $K\bar K_1(1400)$ with $J^{PC}=1^{--}$ and $K\bar K_1(1270)$ with $J^{PC}=1^{-\pm}$, are also investigated, some of which can be searched for in the future experiments.

hep-ph↗

arXiv2022

Two dynamical generated $a_0$ resonances by interactions between vector mesons

We study dynamically generated $a_0$ resonances by interactions between vector mesons including their coupling to channels of pseudoscalar mesons within coupled-channel approach. Both vector and pseudoscalar mesons are considered as $t$-channel exchanged mesons for calculating interactions between vector mesons. Analogous to $a_0(980)$ as a $K\bar K-πη$ dynamically generated state, there is an $a_0(1710)$ as a coupled channel dynamically generated state near $K^*\bar{K}^*$ threshold. The channels involved are $ρϕ,K^*\bar{K}^*,ρω, K\bar{K},πη$. This $a_0$ mainly decays to $ρω$, $πη$ and $K\bar{K}$. This pole is much tied to the coupled channel effect. If we turn off either $ρϕ$ or $K^*\bar{K}^*$, the pole disappears. In addition, it is found that $a_0(1450)$ may also be dynamically generated by $ρω$ interactions due to $π$ and $η$ exchange.

hep-ph↗

arXiv2021

Coupled-channel effects of the $Σ_c^{()}\bar{D}^{()}$-$Λ_c(2595)\bar{D}$ system and molecular nature of the $P_c$ pentaquark states from one-boson exchange model

The effects of the $Σ_c\bar{D}^*$-$Λ_{c}(2595)\bar{D}$ coupled-channel dynamics and various one-boson-exchange (OBE) forces for the LHCb pentaquark states, $P_c(4440)$ and $P_c(4457)$, are reinvestigated. Both the pion and $ρ$-meson exchanges are considered for the $Σ_c\bar{D}^*$-$Λ_{c}(2595)\bar{D}$ coupled-channel dynamics. It is found that the role of the $Λ_{c}(2595)\bar{D}$ channel in the descriptions of the $P_c(4440)$ and $P_c(4457)$ states is not significant with the OBE parameters constrained by other experimental sources. The naive OBE models with the short-distance $δ(\vec{r})$ term of the one-pion exchange (OPE) keep failing to reproduce the $P_c(4440)$ and $P_c(4457)$ states simultaneously. The OPE potential with the full $δ(\vec{r})$ term results in a too large mass splitting for the $J^P=1/2^-$ and $3/2^-$ $Σ_c\bar{D}^*$ bound states with total isospin $I=1/2$. The OBE model with only the OPE $δ(\vec{r})$ term dropped may fit the splitting much better but somewhat underestimates the splitting. Since the $δ(\vec r)$ potential is from short-distance physics, which also contains contributions from the exchange of mesons heavier than those considered explicitly, we vary the strength of the $δ(\vec r)$ potential and find that the masses of the $P_c(4312)$, $P_c(4440)$, and $P_c(4457)$ can be reproduced simultaneously with the $δ(\vec r)$ term in the OBE model reduced by about 80\%. While two different spin assignments are possible to produce their masses, in the preferred description, the spin parities of the $P_c(4440)$ and $P_c(4457)$ are $3/2^-$ and $1/2^-$, respectively.

hep-ph↗

arXiv2021

A survey of heavy-heavy hadronic molecules

The spectrum of hadronic molecules composed of heavy-antiheavy charmed hadrons has been obtained in our previous work. The potentials are constants at the leading order, which are estimated from resonance saturation. The experimental candidates of hadronic molecules, say $X(3872)$, $Y(4260)$, three $P_c$ states and $P_{cs}(4459)$, fit the spectrum well. The success in describing the pattern of heavy-antiheavy hadronic molecules stimulates us to give more predictions for the heavy-heavy cases, which are less discussed in literature than the heavy-antiheavy ones. Given that the heavy-antiheavy hadronic molecules, several of which have strong experimental evidence, emerge from the dominant constant interaction from resonance saturation, we find that the existence of many heavy-heavy hadronic molecules is natural. Among these predicted heavy-heavy states we highlight the $DD^*$ molecule and the $D^{(*)}Σ_c^{(*)}$ molecules, which are the partners of the famous $X(3872)$ and $P_c$ states. Quite recently, LHCb collaboration reported a doubly charmed tetraquark state, $T_{cc}$, which is in line with our results for the $DD^*$ molecule. With the first experimental signal of this new kind of exotic states, the upcoming 3pdate of the LHCb experiment as well as other experiments will provide more chances of observing the heavy-heavy hadronic molecules.

hep-ph↗

arXiv2021

Is the existence of a $J/ψJ/ψ$ bound state plausible?

In a recent measurement LHCb reported pronounced structures in the $J/ψJ/ψ$ spectrum. One of the various possible explanations of those is that they emerge from non-perturbative interactions of vector charmonia. It is thus important to understand whether it is possible to form a bound state of two charmonia interacting through the exchange of gluons, which hadronise into two pions at the longest distance. In this paper, we demonstrate that, given our current understanding of hadron-hadron interactions, the exchange of correlated light mesons (pions and kaons) is able to provide sizeable attraction to the di-$J/ψ$ system, and it is possible for two $J/ψ$ mesons to form a bound state. As a side result we find from an analysis of the data for the $ψ(2S)\to J/ψππ$ transition including both $ππ$ and $K\bar K$ final state interactions an improved value for the $ψ(2S)\to J/ψ$ transition chromo-electric polarisability: $|α_{ψ(2S)J/ψ}|= (1.8\pm 0.1)~\mbox{GeV}^{-3}$, where the uncertainty also includes the one induced by the final state interactions.

hep-ph↗

arXiv2021

A survey of heavy-antiheavy hadronic molecules

Many efforts have been made to reveal the nature of the overabundant resonant structures observed by the worldwide experiments in the last two decades. Hadronic molecules attract special attention because many of these seemingly unconventional resonances are located close to the threshold of a pair of hadrons. To give an overall feature of the spectrum of hadronic molecules composed of a pair of heavy-antiheavy hadrons, namely, which pairs are possible to form molecular states, we take charmed hadrons for example to investigate the interaction between them and search for poles by solving the Bethe-Salpeter equation. We consider all possible combinations of hadron pairs of the $S$-wave singly-charmed mesons and baryons as well as the narrow $P$-wave charmed mesons. The interactions, which are assumed to be meson-exchange saturated, are described by constant contact terms which are resummed to generate poles. It turns out that if a system is attractive near threshold by the light meson exchange, there is a pole close to threshold corresponding to a bound state or a virtual state, depending on the strength of interaction and the cutoff. In total, 229 molecular states are predicted. The observed near-threshold structures with hidden-charm, like the famous $X(3872)$ and $P_c$ states, fit into the spectrum we obtain. We also highlight a $Λ_c\bar Λ_c$ bound state that has a pole consistent with the cross section of the $e^+e^-\toΛ_c\bar Λ_c$ precisely measured by the BESIII Collaboration.

hep-ph↗