Showing papers by "Xiang Liu published in 2019"
TL;DR: Recently, the LHCb collaboration not only confirmed the existence of the hidden-charm pentaquarks, but also provided strong evidence of the molecular picture as discussed by the authors, where the authors reviewed the experimental and theoretical efforts on the hidden heavy flavor multiquark systems in the past three years.
465 citations
TL;DR: In this paper, the experimental and theoretical efforts on the hidden heavy flavor multiquark systems in the past three years were reviewed extensively in [Phys. Rept. 639 (2016) 1-121].
Abstract: The past seventeen years have witnessed tremendous progress on the experimental and theoretical explorations of the multiquark states. The hidden-charm and hidden-bottom multiquark systems were reviewed extensively in [Phys. Rept. 639 (2016) 1-121]. In this article, we shall update the experimental and theoretical efforts on the hidden heavy flavor multiquark systems in the past three years. Especially the LHCb collaboration not only confirmed the existence of the hidden-charm pentaquarks but also provided strong evidence of the molecular picture. Besides the well-known $XYZ$ and $P_c$ states, we shall discuss more interesting tetraquark and pentaquark systems either with one, two, three or even four heavy quarks. Some very intriguing states include the fully heavy exotic tetraquark states $QQ\bar Q\bar Q$ and doubly heavy tetraquark states $QQ\bar q \bar q$, where $Q$ is a heavy quark. The $QQ\bar Q\bar Q$ states may be produced at LHC while the $QQ\bar q \bar q$ system may be searched for at BelleII and LHCb. Moreover, we shall pay special attention to various theoretical schemes. We shall emphasize the model-independent predictions of various models which are truly/closely related to Quantum Chromodynamics (QCD). There have also accumulated many lattice QCD simulations through multiple channel scattering on the lattice in recent years, which provide deep insights into the underlying structure/dynamics of the $XYZ$ states. In terms of the recent $P_c$ states, the lattice simulations of the charmed baryon and anti-charmed meson scattering are badly needed. We shall also discuss some important states which may be searched for at BESIII, BelleII and LHCb in the coming years.
339 citations
TL;DR: In this paper, the authors present a direct calculation by the one-boson exchange model and demonstrate explicitly that the loosely bound molecular hidden-charm pentaquark states composed of an $S$-wave charmed baryon and an anticharmed meson do correspond to the loosely bounded nonsmooth baryons.
Abstract: On 26 March 2019, at the Rencontres de Moriond QCD conference, the LHCb Collaboration reported the observation of three new pentaquarks, namely ${P}_{c}(4312)$, ${P}_{c}(4440)$, and ${P}_{c}(4457)$, which are consistent with the loosely bound molecular hidden-charm pentaquark states composed of an $S$-wave charmed baryon ${\mathrm{\ensuremath{\Sigma}}}_{c}$ and an $S$-wave anticharmed meson ($\overline{D}$, ${\overline{D}}^{*}$). In this work, we present a direct calculation by the one-boson-exchange model and demonstrate explicitly that the ${P}_{c}(4312)$, ${P}_{c}(4440)$, and ${P}_{c}(4457)$ do correspond to the loosely bound ${\mathrm{\ensuremath{\Sigma}}}_{c}\overline{D}$ with ($I=1/2$, ${J}^{P}=1/{2}^{\ensuremath{-}}$), ${\mathrm{\ensuremath{\Sigma}}}_{c}{\overline{D}}^{*}$ with ($I=1/2$, ${J}^{P}=1/{2}^{\ensuremath{-}}$), and ${\mathrm{\ensuremath{\Sigma}}}_{c}{\overline{D}}^{*}$ with ($I=1/2$, ${J}^{P}=3/{2}^{\ensuremath{-}}$), respectively.
176 citations
TL;DR: In this paper, the potentials of the D{D}^{*} system up to the one-loop level were studied in the framework of heavy meson chiral effective field theory and the contact and two-pion exchange interactions were investigated.
Abstract: The $D{D}^{*}$ potentials are studied within the framework of heavy meson chiral effective field theory. We obtain the effective potentials of the $D{D}^{*}$ system up to $O({\ensuremath{\epsilon}}^{2})$ at the one-loop level. In addition to the one-pion exchange contribution, the contact and two-pion exchange interactions are also investigated in detail. Furthermore, we search for the possible molecular states by solving the Schr\"odinger equation with the potentials. We notice that the contact and two-pion exchange potentials are numerically non-negligible and important for the existence of a bound state. In our results, no bound state is found in the $I=0$ channel within a wide range of the cutoff parameter, while there exists a bound state in the $I=1$ channel as the cutoff is near ${m}_{\ensuremath{\rho}}$ in our approach.
53 citations
TL;DR: Based on the updated data of charmonium-like state $Y(4220)$ reported in the hidden-charm channels of the ${e}+}{e}^{\ensuremath{-}}$ annihilation, this paper proposed a $4S$-$3D$ mixing scheme to categorize the CHARMIA into the $J/
Abstract: Based on the updated data of charmoniumlike state $Y(4220)$ reported in the hidden-charm channels of the ${e}^{+}{e}^{\ensuremath{-}}$ annihilation, we propose a $4S$-$3D$ mixing scheme to categorize $Y(4220)$ into the $J/\ensuremath{\psi}$ family. We find that the present experimental data can support this charmonium assignment to $Y(4220)$. Thus, $Y(4220)$ plays a role of a scaling point in constructing higher charmonia above 4 GeV. To further test this scenario, we provide more abundant information on the decay properties of $Y(4220)$, and predict its charmonium partner $\ensuremath{\psi}(4380)$, whose evidence is found by analyzing the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\psi}(3686){\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ data from BESIII. If $Y(4220)$ is indeed a charmonium, we must face how to settle the established charmonium $\ensuremath{\psi}(4415)$ in the $J/\ensuremath{\psi}$ family. In this work, we may introduce a $5S$-$4D$ mixing scheme, and obtain the information of the resonance parameters and partial open-charm decay widths of $\ensuremath{\psi}(4415)$, which do not contradict the present experimental data. Additionally, we predict a charmonium partner $\ensuremath{\psi}(4500)$ of $\ensuremath{\psi}(4415)$, which can be accessible at future experiments, especially, BESIII and BelleII. The studies presented in this work provide new insights to establish the higher charmonium spectrum.
49 citations
TL;DR: In this paper, the mass splittings of tetraquark states with chromomagnetic interactions between their quark components were studied and a defined measure reflecting effective quark interactions was obtained.
Abstract: We study the mass splittings of ${Q}_{1}{q}_{2}{\overline{Q}}_{3}{\overline{q}}_{4}$ ($Q=c$, $b$, $q=u$, $d$, $s$) tetraquark states with chromomagnetic interactions between their quark components. Assuming that $X(4140)$ is the lowest ${J}^{PC}={1}^{++}\text{ }\text{ }cs\overline{c}\overline{s}$ tetraquark, we estimate the masses of the other tetraquark states. From the obtained masses and defined measure reflecting effective quark interactions, we find the following assignments for several exotic states: (1) both $X(3860)$ and the newly observed ${Z}_{c}(4100)$ seem to be ${0}^{++}\text{ }\text{ }cn\overline{c}\overline{n}$ tetraquarks; (2) ${Z}_{c}(4200)$ is probably a ${1}^{+\ensuremath{-}}\text{ }\text{ }cn\overline{c}\overline{n}$ tetraquark; (3) ${Z}_{c}(3900)$, $X(3940)$, and $X(4160)$ are unlikely compact tetraquarks; (4) ${Z}_{c}(4020)$ is unlikely a compact tetraquark, but seems the hidden-charm correspondence of ${Z}_{b}(10650)$ with ${J}^{PC}={1}^{+\ensuremath{-}}$; and (5) ${Z}_{c}(4250)$ can be a tetraquark candidate but the quantum numbers cannot be assigned at present. We hope further studies may check the predictions and assignments given here.
49 citations
TL;DR: In this article, the intermeson interactions of double-beauty systems have been studied with heavy meson chiral effective field theory up to one-loop level, and the effective potentials are calculated with Weinberg's scheme up to the level of four-body contact interactions and one-pion exchange contributions.
Abstract: In this work, the intermeson interactions of double-beauty $\overline{B}\overline{B}$, $\overline{B}{\overline{B}}^{*}$, and ${\overline{B}}^{*}{\overline{B}}^{*}$ systems have been studied with heavy meson chiral effective field theory. The effective potentials are calculated with Weinberg's scheme up to one-loop level. At the leading order, four-body contact interactions and one-pion exchange contributions are considered. In addition to two-pion exchange diagrams, we include the one-loop chiral corrections to contact terms and one-pion exchange diagrams at the next-to-leading order. The behaviors of effective potentials, both in momentum space and coordinate space, are investigated and discussed extensively. We notice the contact terms play important roles in determining the characteristics of the total potentials. Only the potentials in $I({J}^{P})=0({1}^{+})$ $\overline{B}{\overline{B}}^{*}$ and ${\overline{B}}^{*}{\overline{B}}^{*}$ systems are attractive, and the corresponding binding energies in these two channels are solved to be $\mathrm{\ensuremath{\Delta}}{E}_{\overline{B}{\overline{B}}^{*}}\ensuremath{\simeq}\ensuremath{-}{12.6}_{\ensuremath{-}12.9}^{+9.2}\text{ }\text{ }\mathrm{MeV}$ and $\mathrm{\ensuremath{\Delta}}{E}_{{\overline{B}}^{*}{\overline{B}}^{*}}\ensuremath{\simeq}\ensuremath{-}{23.8}_{\ensuremath{-}21.5}^{+16.3}\text{ }\text{ }\mathrm{MeV}$, respectively. The masses of $0({1}^{+})$ $\overline{B}{\overline{B}}^{*}$ and ${\overline{B}}^{*}{\overline{B}}^{*}$ states lie above the threshold of their electromagnetic decay modes $\overline{B}\overline{B}\ensuremath{\gamma}$ and $\overline{B}\overline{B}\ensuremath{\gamma}\ensuremath{\gamma}$, and thus they can be reconstructed via electromagnetic interactions. Our calculation not only provides some useful information to explore exotic doubly bottomed molecular states for future experiments, but also is helpful for the extrapolations of Lattice QCD simulations.
37 citations
TL;DR: In this paper, the predicted masses and decay widths of the bottom baryons of the LHCb were analyzed and the possible explanations for the difficulty of decoding the signals were discussed.
Abstract: The measured masses and strong decays of ${\mathrm{\ensuremath{\Lambda}}}_{b}(6146{)}^{0}$ and ${\mathrm{\ensuremath{\Lambda}}}_{b}(6152{)}^{0}$ required us to decode them as the $1D$ excited states with ${J}^{P}=3/{2}^{+}$ and ${J}^{P}=5/{2}^{+}$, respectively. Under the suggested assignment, the masses and total decay widths of ${\mathrm{\ensuremath{\Lambda}}}_{b}(6146{)}^{0}$ and ${\mathrm{\ensuremath{\Lambda}}}_{b}(6152{)}^{0}$ can be explained. As a ${J}^{P}=3/{2}^{+}$ state, the ${\mathrm{\ensuremath{\Lambda}}}_{b}(6146{)}^{0}$ should mainly decay into ${\mathrm{\ensuremath{\Sigma}}}_{b}(5815)\ensuremath{\pi}$. However, this theoretical result is in contradiction to the measurement since no significant ${\mathrm{\ensuremath{\Lambda}}}_{b}(6146{)}^{0}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Sigma}}}_{b}(5815{)}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\pi}}^{\ensuremath{\mp}}$ signals were observed by the LHCb. The possible explanations for this difficulty are mentioned. For completeness, we present the prediction of masses and decay widths of other unseen $1D$ bottom baryons in this work. Our results could provide some important clues for the upcoming experiments.
33 citations
TL;DR: In this article, the authors explore the possibility of forming a doubly charmed baryon and a charmed meson in a doublet with the heavy quark spin symmetry.
Abstract: In this work, we explore a systematic investigation on $S$-wave interactions between a doubly charmed baryon ${\mathrm{\ensuremath{\Xi}}}_{cc}(3621)$ and a charmed meson in a $T$ doublet $({D}_{1},{D}_{2}^{*})$. We first analyze the possibility for forming ${\mathrm{\ensuremath{\Xi}}}_{cc}{D}_{1}/{\mathrm{\ensuremath{\Xi}}}_{cc}{D}_{2}^{*}$ bound states with the heavy quark spin symmetry. Then, we further perform a dynamical study on the ${\mathrm{\ensuremath{\Xi}}}_{cc}{D}_{1}/{\mathrm{\ensuremath{\Xi}}}_{cc}{D}_{2}^{*}$ interactions within a one-boson-exchange model by considering both the $S\ensuremath{-}D$ wave mixing and coupled channel effect. Finally, our numerical results conform the proposals from the heavy quark spin symmetry analysis: the ${\mathrm{\ensuremath{\Xi}}}_{cc}{D}_{1}$ systems with $I({J}^{P})=0(1/{2}^{+},3/{2}^{+})$ and the ${\mathrm{\ensuremath{\Xi}}}_{cc}{D}_{2}^{*}$ systems with $I({J}^{P})=0(3/{2}^{+},5/{2}^{+})$ can possibly be loose triple-charm molecular pentaquarks. Meanwhile, we also extend our model to the ${\mathrm{\ensuremath{\Xi}}}_{cc}{\overline{D}}_{1}$ and ${\mathrm{\ensuremath{\Xi}}}_{cc}{\overline{D}}_{2}^{*}$ systems, and our results indicate the isoscalars of ${\mathrm{\ensuremath{\Xi}}}_{cc}{\overline{D}}_{1}$ and ${\mathrm{\ensuremath{\Xi}}}_{cc}{\overline{D}}_{2}^{*}$ can be possible molecular candidates.
26 citations
TL;DR: In this paper, the authors investigated the spectrum and the two-body strong decays allowed by the Okubo-Zweig-Iizuka rule for the unflavored light meson families.
Abstract: The unflavored light meson families, namely, ${\ensuremath{\omega}}_{2}$, ${\ensuremath{\rho}}_{2}$, and ${\ensuremath{\phi}}_{2}$, are studied systematically by investigating the spectrum and the two-body strong decays allowed by the Okubo-Zweig-Iizuka rule. Including the four experimentally observed states and other predicted states, phenomenological analysis of the partial decay widths can verify the corresponding assignments of these states into the families. Moreover, we provide typical branching ratios of the dominant decay channels, especially for missing ground states, which is helpful to search for or confirm them and explore more properties of these families in experiments.
22 citations
TL;DR: In this article, the decay of the charged heavy quarkonium-like states was investigated and the decay ratios were compared with the experimental data, which are useful in judging whether the molecule state assignment for the corresponding states is reasonable or not.
Abstract: Employing the relativized quark model and the quark-interchange model, we investigate the decay of the charged heavy quarkonium-like states $$Z_c(3900)$$
, $$Z_c(4020)$$
, $$Z_c(4430)$$
, $$Z_b(10610)$$
and $$Z_b(10650)$$
into the ground and radially excited heavy quarkonia via emitting a pion meson. The $$Z_c$$
and $$Z_b$$
states are assumed to be hadronic molecules composed of open-flavor heavy mesons. The calculated decay ratios can be compared with the experimental data, which are useful in judging whether the molecule state assignment for the corresponding $$Z_c$$
or $$Z_b$$
state is reasonable or not. The theoretical framework constructed in this work will be helpful in revealing the underlying structures of some exotic hadrons.
TL;DR: In this paper, the mass splittings for the triply heavy pentaquark states with the configuration $qqQQ\overline{Q}$ were systematically calculated in the framework of the color-magnetic interaction model and their masses were estimated and their stabilities were discussed according to possible rearrangement decay patterns.
Abstract: In the framework of the color-magnetic interaction model, we systematically calculate the mass splittings for the $S$-wave triply heavy pentaquark states with the configuration $qqQQ\overline{Q}$ $(Q=c,b;\phantom{\rule{0ex}{0ex}}q=u,d,s)$. Their masses are estimated and their stabilities are discussed according to possible rearrangement decay patterns. Our results indicate that there may exist several stable or narrow such states. We hope the present study can help experimentalists search for exotic pentaquarks.
TL;DR: For the long standing low mass puzzle of $\Lambda_c(2940)^+$, this article proposed an unquenched picture, which explicitly showed that the mass of the 2P,3/2^-)$ state can be lowered down to be consistent with the experimental data by introducing the $D^*N$ channel contribution.
Abstract: For the long standing low mass puzzle of $\Lambda_c(2940)^+$, we propose an unquenched picture. Our calculation explicitly shows that the mass of the $\Lambda_c(2P,3/2^-)$ state can be lowered down to be consistent with the experimental data of $\Lambda_c(2940)^+$ by introducing the $D^*N$ channel contribution. Additionally, we give a semi-quantitative analysis to illustrate why the $\Lambda_c(2940)^+$ state has a narrow width. It means that the low mass puzzle of $\Lambda_c(2940)^+$ can be solved. What is more important is that we predict a mass inversion relation for the $2P$ $\Lambda_{c}^+$ states, i.e., the $\Lambda_c(2P,1/2^-)$ state is higher than the $\Lambda_c(2P,3/2^-)$, which is totally different from the result of conventional quenched quark model. It provides a criterion to test such an unquenched scenario for $\Lambda_c(2940)^+$. We expect the future experimental progress from the LHCb and Belle II.
TL;DR: In this article, the authors performed a combined fit to the experimental data of the cross-section of the mass spectrum and the corresponding dipion invariant mass spectra and showed that the observed charged charmonium-like structure can be well reproduced based on the initial single pion emission (ISPE) mechanism.
Abstract: In 2017, the BESIII Collaboration announced the observation of a charged charmonium-like structure in the $$\psi (3686)\pi ^\pm $$
invariant mass spectrum of the $$e^+ e^- \rightarrow \psi (3686) \pi ^+ \pi ^-$$
process at different energy points, which enables us to perform a precise study of this process based on the initial single pion emission (ISPE) mechanism. In this work, we perform a combined fit to the experimental data of the cross section of $$e^+ e^- \rightarrow \psi (3686) \pi ^+ \pi ^-$$
, and the corresponding $$\psi (3686)\pi ^\pm $$
and dipion invariant mass spectra. Our result shows that the observed charged charmonium-like structure in $$e^+ e^- \rightarrow \psi (3686) \pi ^+ \pi ^-$$
can be well reproduced based on the ISPE mechanism, and that the corresponding dipion invariant mass spectrum and cross section can be depicted with the same parameters. In fact, it provides strong evidence that the ISPE mechanism can be an underlying mechanism resulting in such novel a phenomenon.
TL;DR: In this article, the authors performed a systematic study on the interaction of an antistrange meson with a ground octet baryon, where the spin-orbit force and the recoil correction were considered in the adopted one-boson exchange model.
Abstract: The newly observed $\mathrm{\ensuremath{\Xi}}(1620{)}^{0}$ by the Belle Collaboration inspires our interest in performing a systematic study on the interaction of an antistrange meson $({\overline{K}}^{(*)})$ with a strange or doubly strange ground octet baryon $\mathcal{B}$ ($\mathrm{\ensuremath{\Lambda}}$, $\mathrm{\ensuremath{\Sigma}}$, and $\mathrm{\ensuremath{\Xi}}$), where the spin-orbit force and the recoil correction are considered in the adopted one-boson-exchange model. Our results indicate that $\mathrm{\ensuremath{\Xi}}(1620{)}^{0}$ can be explained as a $\overline{K}\mathrm{\ensuremath{\Lambda}}$ molecular state with $I({J}^{P})=1/2(1/{2}^{\ensuremath{-}})$ and the intermediate force from $\ensuremath{\sigma}$ exchange plays an important role. Additionally, we also predict several other possible molecular candidates, i.e., the $\overline{K}\mathrm{\ensuremath{\Sigma}}$ molecular state with $I({J}^{P})=1/2(1/{2}^{\ensuremath{-}})$ and the triply strange $\overline{K}\mathrm{\ensuremath{\Xi}}$ molecular state with $I({J}^{P})=0(1/{2}^{\ensuremath{-}})$.
TL;DR: In this paper, the authors performed a combined fit to the experimental data of the cross section of the $e^+ e^- \to \psi(3686) \pi^+ \pi-$, and the corresponding dipion invariant mass spectrum and cross section can be depicted with the same parameters.
Abstract: In 2017, the BESIII Collaboration announced the observation of a charged charmonium-like structure in the $\psi(3686)\pi^\pm$ invariant mass spectrum of the $e^+ e^- \to \psi(3686) \pi^+ \pi^-$ process at different energy points, which enables us to perform a precise study of this process based on the initial single pion emission (ISPE) mechanism. In this work, we perform a combined fit to the experimental data of the cross section of $e^+ e^- \to \psi(3686) \pi^+ \pi^-$, and the corresponding $\psi(3686)\pi^\pm$ and dipion invariant mass spectra. Our result shows that the observed charged charmonium-like structure in $e^+ e^- \to \psi(3686) \pi^+ \pi^-$ can be well reproduced based on the ISPE mechanism, and that the corresponding dipion invariant mass spectrum and cross section can be depicted with the same parameters. In fact, it provides strong evidence that the ISPE mechanism can be an underlying mechanism resulting in such novel a phenomenon.
TL;DR: In this paper, the covariant light-front approach with conventional vertex functions was used to estimate the production rates of D-wave charmed/charmed-strange mesons via the semileptonic decays.
Abstract: Using the covariant light-front approach with conventional vertex functions, we estimate the production rates of D -wave charmed/charmed-strange mesons via the \begin{document}$B_{(s)}$\end{document} semileptonic decays. As the calculated production rates are significant, it seems possible to experimentally search for D -wave charmed/charmed-strange mesons via semileptonic decays, which may provide an additional approach for exploring D -wave charmed/charmed-strange mesons.
Posted Content•
TL;DR: In this paper, the interactions between two heavy mesons within heavy meson chiral effective field theory and investigated possible molecular states were studied. And the effective potentials were obtained with Weinberg's scheme up to one-loop level.
Abstract: We have studied the interactions between two heavy mesons ($D^{(*)}$-$D^{(*)}$, $\bar D^{(*)}$-$\bar D^{(*)}$, $B^{(*)}$-$B^{(*)}$, or $\bar B^{(*)}$-$\bar B^{(*)}$) within heavy meson chiral effective field theory and investigated possible molecular states. The effective potentials are obtained with Weinberg's scheme up to one-loop level. At the leading order, four body contact interactions and one pion exchange contributions are considered. In addition to two pion exchange diagrams, we include the one-loop chiral corrections to contact terms and one pion exchange diagrams at the next-to-leading order. The effective potentials both in momentum space and coordinate space are investigated and discussed extensively. The possible molecular states are also studied and the binding energies are provided by solving the Schrodinger equation. The results will be helpful for the experimental search for the doubly-heavy molecular states.