arXiv subjects

Feng-Kun Guo

Publications and source records attributed to Feng-Kun Guo.

At least 109 records · Page 6Linked to original sources

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.

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arXiv2022

A combined analysis of the $Z_c(3900)$ and the $Z_{cs}(3985)$ exotic states

We have performed a combined analysis of the BESIII data for both the $Z_c(3900)$ and $Z_{cs}(3985)$ structures, assuming that the latter is an SU(3) flavor partner of the former one. We have improved on the previous analysis of Albaladejo $et$ $al.$ [Phys. Lett. B 755, 337 (2016)] by computing the amplitude for the $D_1\bar{D}D^*$ triangle diagram considering both $D$ and $S$-wave $D_1D^*π$ couplings. We have also investigated effects from SU(3) light-flavor violations, which are found to be moderate and of the order of 20%. The successful reproduction of the BESIII spectra, in both the hidden-charm and hidden-charm strange sectors, strongly supports that the $Z_{cs}(3985)$ and $Z_c(3900)$ are SU(3) flavor partners placed in the same octet multiplet. The best results are obtained when an energy-dependent term in the diagonal $D^{(*)}\bar D_{(s)}^{(*)}$ interaction is included, leading to resonances (poles above the thresholds) to describe these exotic states. We have also made predictions for the isovector $Z_{c}^*$ and isodoublet $Z_{cs}^*$, $D^*\bar{D}^*$ and $D^*\bar{D}_{s}^*$ molecules, with $J^{PC}=1^{+-}$ and $J^{P}=1^{+}$, respectively. These states would be heavy-quark spin symmetry partners of the $Z_{c}$ and $Z_{cs}$. Besides the determination of the masses and widths of the $Z_c(3900)$ and $Z_{cs}(3985)$, we also predict those of the $Z_c^*$ and $Z_{cs}^*$ resonances.

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arXiv2022

Generalization of Weinberg's Compositeness Relations

We generalize the time-honored Weinberg's compositeness relations by including the range corrections through considering a general form factor. In Weinberg's derivation, he considered the effective range expansion up to $\mathcal{O}(p^2)$ and made two additional approximations: neglecting the non-pole term in the Low equation; approximating the form factor by a constant. We lift the second approximation, and work out an analytic expression for the form factor. For a positive effective range, the form factor is of a single-pole form. An integral representation of the compositeness is obtained and is expected to have a smaller uncertainty than that derived from Weinberg's relations. We also establish an exact relation between the wave function of a bound state and the phase of the scattering amplitude neglecting the non-pole term. The deuteron is analyzed as an example, and the formalism can be applied to other cases where range corrections are important.

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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.

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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.

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arXiv2022

Hadron spectroscopy at STCF

Despite that quantum chromodynamics, the theory of strong interaction, has colorful quarks and gluons as its basic degrees of freedom, all fundamental particles participating the strong interaction that can be directly detected in experiments are colorless or color-singlet hadrons. This phenomenon is called color confinement. Because of that, the study of hadron spectroscopy is essential in improving our understanding of the nonperturbative regime of QCD and to reveal the mechanism of color confinement. The high-luminosity electron-positron collision machine under discussion, Super tau-Charm Facility (STCF), can play an essential role in hadron spectroscopy by discovering new hadron resonances and measuring properties of known hadrons with an unprecedented precision. In the following, we will discuss briefly the topics on hadron spectroscopy that will be investigated at STCF.

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arXiv2022

Effective range expansion for narrow near-threshold resonances

We discuss some general features of the effective range expansion, the content of its parameters with respect to the nature of the pertinent near-threshold states and the necessary modifications in the presence of coupled channels, isospin violations and unstable constituents. As illustrative examples, we analyse the properties of the $χ_{c1}(3872)$ and $T_{cc}^+$ states supporting the claim that these exotic states have a predominantly molecular nature.

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arXiv2022

Pion axioproduction: The Delta resonance contribution

The process of pion axioproduction, $aN\toπN$, with an intermediate $Δ$ resonance is analyzed using baryon chiral parturbation theory. The $Δ$ resonance is included in two ways: First, deriving the $aΔN$-vertices, the axion is brought into contact with the resonance, and, second, taking the results of $πN$ elastic scattering including the $Δ$, it is implicitly included in the form of a pion rescattering diagram. As a result, the partial wave cross section of axion-nucleon scattering shows an enhancement in the energy region around the $Δ$ resonance. Because of the isospin breaking, the enhancement is not as pronounced as previously anticipated. However, since the isospin breaking here is much milder than that for usual hadronic processes, novel axion search experiments might still exploit this effect.

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arXiv2022

$D^+D^-$ hadronic atom and its production in $pp$ and $p\bar{p}$ collisions

There must be Coulomb bound states of a pair of hadrons, which are stable against the strong interaction, with opposite electric charges. Such bound states are hadronic atoms. We study the properties and the production of the ground-state $D^+D^-$ hadronic atom $A_{D^+D^-}$, called dionium, with quantum numbers $J^{PC}=0^{++}$. Using a nonrelativistic effective field theory for the $D^0\bar{D}^0$-$D^+D^-$ coupled-channel system, the mass of the ground-state dionium is predicted to be $(3739.3 \pm 0.1)~\text{MeV}$, with the binding energy reduced by about 10% compared to the Coulomb binding energy due to the strong interaction. Its width for the decay into the neutral $D^0\bar D^0$ channel is predicted to be $1.8^{+1.4}_{-0.6}$ keV using lattice inputs for the $D\bar D$ strong interaction. The cross section for the inclusive prompt production of the dionium at CMS and LHCb and that for the direct production $p\bar p\to A_{D^+D^-}$ at PANDA are estimated at an order-of-magnitude level. In particular, we expect that $\mathcal{O}(10^3\sim 10^5)$ events of the reaction chain $p\bar p\to A_{D^+D^-}\to D^0\bar D^0 \to K^-π^+K^+π^-$ can be collected at PANDA, and valuable information on the charmed meson interaction and on understanding charmoniumlike states will be obtained.

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arXiv2022

Coupled-channel approach to $T_{cc}^+$ including three-body effects

A coupled-channel approach is applied to the charged tetraquark state $T_{cc}^+$ recently discovered by the LHCb Collaboration. The parameters of the interaction are fixed by a fit to the observed line shape in the three-body $D^0D^0π^+$ channel. Special attention is paid to the three-body dynamics in the $T_{cc}^+$ due to the finite life time of the $D^*$. An approach to the $T_{cc}^+$ is argued to be self-consistent only if both manifestations of the three-body dynamics, the pion exchange between the $D$ and $D^*$ mesons and the finite $D^*$ width, are taken into account simultaneously to ensure that three-body unitarity is preserved. This is especially important to precisely extract the pole position in the complex energy plane whose imaginary part is very sensitive to the details of the coupled-channel scheme employed. The $D^0D^0$ and $D^0D^+$ invariant mass distributions, predicted based on this analysis, are in good agreement with the LHCb data. The low-energy expansion of the $D^*D$ scattering amplitude is performed and the low-energy constants (the scattering length and effective range) are extracted. The compositeness parameter of the $T_{cc}^+$ is found to be close to unity, which implies that the $T_{cc}^+$ is a hadronic molecule generated by the interactions in the $D^{*+}D^0$ and $D^{*0}D^+$ channels. Employing heavy-quark spin symmetry, an isoscalar $D^*D^*$ molecular partner of the $T_{cc}^+$ with $J^P=1^+$ is predicted under the assumption that the $ DD^*$-$D^*D^*$ coupled-channel effects can be neglected.

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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.

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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.

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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.

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arXiv2021

Semi-inclusive lepto-production of hidden-charm exotic hadrons

We investigate the semi-inclusive production of hidden-charm exotic states, including $X(3872)$, $Z_c$, $Z_{cs}$ and the pentaquark $P_c$ states, in lepton-proton scattering processes. These hadrons are close to the thresholds of a pair of charm and anticharm hadrons, and are assumed to have hadronic molecular structure as their main components. In order to give order-of-magnitude estimates of the cross sections, we use Pythia to simulate the short-distance productions of the constituent hadrons, which then rescatter to form the exotic hadrons. The estimates for the $X(3872)$ and $Z_c(3900)^\pm$ are not in conflict with the upper limits measured at the COMPASS experiment for the exclusive photoproduction process. The results here indicate that the considered hidden-charm states can be copiously produced at the proposed electron-ion colliders EicC and US-EIC.

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arXiv2021

Coupled-channel interpretation of the LHCb double-$J/ψ$ spectrum and hints of a new state near the $J/ψJ/ψ$ threshold

Recently, the LHCb Collaboration reported pronounced structures in the invariant mass spectrum of $J/ψ$-pairs produced in proton-proton collisions at the Large Hadron Collider. In this Letter, we argue that the data can be very well described within two variants of a coupled-channel approach employing $T$-matrices consistent with unitarity: (i) with just two channels, $J/ψJ/ψ$ and $ψ(2S)J/ψ$, as long as energy-dependent interactions in these channels are allowed, or (ii) with three channels $J/ψJ/ψ$, $ψ(2S)J/ψ$ and $ψ(3770)J/ψ$ with just constant contact interactions. Both formulations hint at the existence of a near-threshold state in the $J/ψJ/ψ$ system with the quantum numbers $J^{PC}=0^{++}$ or $2^{++}$, which we refer to as $X(6200)$. We suggest experimental tests to check the existence of this state and discuss what additional channels need to be studied experimentally to allow for distinctive tests between the two mechanisms proposed. If the molecular nature of the $X(6200)$, as hinted by the three-channel approach, is confirmed, many other double-quarkonium states should exist driven by the same binding mechanism. In particular, there should be an $η_cη_c$ molecule with a similar binding energy.

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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.

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arXiv2021

Revisiting the nature of the $P_c$ pentaquarks

The nature of the three narrow $P_c$ states, i.e., $P_c(4312)$, $P_c(4440)$ and $P_c(4457)$, is under intense discussion since their discovery from the updated analysis by LHCb. In this work we extend our previous coupled-channel approach [Phys. Rev. Lett. \bf{124}, 072001 (2020)] by including the $Λ_c\bar{D}^{(*)}$ and $η_cp$ as explicitly in addition to the $J/ψp$, as required by unitarity and heavy quark spin symmetry (HQSS). Since inelastic parameters are very badly constrained by the current data, three schemes are considered: (a) scheme I with pure contact interactions and without the $Λ_c\bar D^{(*)}$ interactions, (b) scheme II, where the one-pion exchange is added to scheme I, and (c) scheme III, where the $Λ_c \bar D^{(*)}$ are included in addition. It is shown that to obtain cutoff independent results, OPE in the multichannel system is to be supplemented with $S$-$D$ mixing contact terms. We demonstrate that the experimental data for the $J/ψp$ invariant mass distribution are consistent with the interpretation of the $P_c(4312)$ and $P_c(4440)/P_c(4457)$ as $Σ_c\bar{D}$ and $Σ_c \bar{D}^{*}$ hadronic molecules, respectively, and that the data show clear evidence for a new narrow $P_c(4380)$, as a $Σ_c^*\bar D$ molecule, which should exist as a consequence of HQSS. While two equally good solutions are found in scheme I, only one of these solutions with the quantum numbers of the $P_c(4440)$ and $P_c(4457)$ being $J^P=3/2^-$ and $1/2^-$, respectively, survives the requirement of regulator independence once the OPE is included. Moreover, we predict the line shapes in the elastic and inelastic channels and demonstrate that those related to the $P_c(4440)$ and the $P_c(4457)$ in the corresponding $Σ_c^{(*)}\bar{D}$ and $η_cp$ mass distributions allow one to confirm the quantum numbers given above, once the data are available.

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arXiv2021

$D^{\pm}D^{*\mp}$ Hadronic Atom as a Key to Revealing the $X(3872)$ Mystery

The $X(3872)$, whose mass coincides with the $D^0\bar D^{*0}$ threshold, is the most extended hadron object. Since its discovery in 2003, debates have never stopped regarding its internal structure. We propose a new object, the $X$ atom, which is the $D^\pm D^{*\mp}$ composite system with positive charge parity and a mass of $(3879.89\pm0.07)$ MeV, formed mainly due to the Coulomb force. We show that a null signal of the $X$ atom can be used to put a lower limit on the binding energy of the $X(3872)$. From the current knowledge of the $X(3872)$ properties, the production rate for the $X$ atom relative to the $X(3872)$ in $B$ decays and at hadron colliders should be at least $1\times10^{-3}$. New insights into the $X(3872)$ will be obtained through studying the $X$ atom.

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