arXiv subjects

Feng-Kun Guo

Publications and source records attributed to Feng-Kun Guo.

At least 91 records · Page 5Linked to original sources

arXiv2024

Production of the $X(4014)$ as the spin-2 partner of $X(3872)$ in $e^+e^-$ collisions

In 2021, the Belle collaboration reported the first observation of a new structure in the $ψ(2S) γ$ final state produced in the two-photon fusion process. In the hadronic molecule picture, this new structure can be associated with the shallow isoscalar $D^*\bar{D}^*$ bound state and as such is an excellent candidate for the spin-2 partner of the $X(3872)$ with the quantum numbers $J^{PC}=2^{++}$ conventionally named $X_2$. In this work we evaluate the electronic width of this new state and argue that its nature is sensitive to its total width, the experimental measurement currently available being unable to distinguish between different options. Our estimates demonstrate that the planned Super $τ$-Charm Facility offers a promising opportunity to search for and study this new state in the invariant mass distributions for the final states $J/ψγ$ and $ψ(2S)γ$.

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arXiv2024

$σ$ exchange in the one-boson exchange model involving the ground state octet baryons

Based on the one-boson-exchange framework that the $σ$ meson serves as an effective parameterization for the correlated scalar-isoscalar $ππ$ interaction, we calculate the coupling constants of the $σ$ to the $\frac{1}{2}^+$ ground state light baryon octet ${\mathbb B}$ by matching the amplitude of ${\mathbb B}\bar{\mathbb B}\toππ\to\bar{\mathbb B}{\mathbb B}$ to that of ${\mathbb B}\bar{\mathbb B}\toσ\to\bar{\mathbb B}{\mathbb B}$. The former is calculated using a dispersion relation, supplemented with chiral perturbation theory results for the ${\mathbb B}{\mathbb B}ππ$ couplings and the Muskhelishvili-Omn\` es representation for the $ππ$ rescattering. Explicitly, the coupling constants are obtained as $g_{NNσ}=8.7_{-1.9}^{+1.7}$, $g_{ΣΣσ}=3.5_{-1.3}^{+1.8}$, $g_{ΞΞσ}=2.5_{-1.4}^{+1.5}$, and $g_{ΛΛσ}=6.8_{-1.7}^{+1.5}$. These coupling constants can be used in the one-boson-exchange model calculations of the interaction of light baryons with other hadrons.

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arXiv2023

Radiative decays of the heavy-quark-spin molecular partner of $T_{cc}^+$

With the assumptions that the $T_{cc}^+$ discovered at LHCb is a $D^{*}D$ hadronic molecule, using a nonrelativistic effective field theory we calculate the radiative partial widths of $T_{cc}^* \to D^*Dγ$ with $T_{cc}^*$ being a $D^{*}D^{*}$ shallow bound state and the heavy-quark-spin partner of $T_{cc}^+$. The $I=0$ $D^*D$ rescattering effect with the $T_{cc}$ pole is taken into account. The results show that the isoscalar $D^{\ast} D$ rescattering can increase the tree-level decay width of $T_{cc}^{\ast +}\rightarrow D^{*+}D^0γ$ by about $50\%$, while decrease that of $T_{cc}^{\ast +}\rightarrow D^{*0}D^+γ$ by a similar amount. The two-body partial decay widths of the $T_{cc}^{*+}$ into $T_{cc}^+γ$ and $T_{cc}^+π^0$ are also calculated, and the results are about $6~\rm{keV}$ and $3~\rm{keV}$, respectively. Considering that the $D^*$ needs to be reconstructed from the $Dπ$ or $Dγ$ final state in an experimental measurement, the four-body partial widths of the $T_{cc}^{*+}$ into $DDγγ$ and $DDπγ$ are explicitly calculated, and we find that the interference effect between different intermediate $D^*Dγ$ states is small. The total radiative decay width of the $T_{cc}^*$ is predicted to be about $24~\rm{keV}$. Adding the hadronic decay widths of $T_{cc}^* \to D^*Dπ$, the total width of the $T_{cc}^*$ is finally predicted to be $(65\pm2)$ keV.

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arXiv2023

Role of left-hand cut contributions on pole extractions from lattice data: Case study for $T_{cc}(3875)^+$

We discuss recent lattice data for the $T_{cc}(3875)^+$ state to stress, for the first time, a potentially strong impact of left-hand cuts from the one-pion exchange on the pole extraction for near-threshold exotic states. In particular, if the left-hand cut is located close to the two-particle threshold, which happens naturally in the $DD^*$ system for the pion mass exceeding its physical value, the effective-range expansion is valid only in a very limited energy range up to the cut and as such is of little use to reliably extract the poles. Then, an accurate extraction of the pole locations requires the one-pion exchange to be implemented explicitly into the scattering amplitudes. Our findings are general and potentially relevant for a wide class of hadronic near-threshold states.

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arXiv2023

Can the two-pole structure of the $D_0^*(2300)$ be understood from recent lattice data?

It was demonstrated in a series of papers employing unitarized chiral perturbation theory that the phenomenology of the scalar open-charm state, the $D_0^*(2300)$, can be understood as the interplay of two poles, corresponding to two scalar-isospin doublet states with different SU(3) flavor content. Within this formalism the lightest open charm positive parity states emerge as being dynamically generated from the scattering of the Goldstone-boson octet off $D$ mesons, a picture that at the same time solves various problems that the experimental observations posed. However, in recent lattice studies of $Dπ$ scattering at different pion masses only one pole was reported in the $D_0^*$ channel, while it was not possible to extract reliable parameters of a second pole from the lattice data. In this paper we demonstrate how this seeming contradiction can be understood and that imposing SU(3) constraints on the fitting amplitudes allows one to extract information on the second pole from the lattice data with minimal bias. The results may also be regarded as a showcase how approximate symmetries can be imposed in the $K$-matrix formalism to reduce the number of parameters.

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arXiv2023

Update on strong and radiative decays of the $D_{s0}^{*}(2317)$ and $D_{s1}(2460)$ and their bottom cousins

The isospin breaking and radiative decay widths of the positive-parity charm-strange mesons, $D^{*}_{s0}$ and $D_{s1}$, and their predicted bottom-strange counterparts, $B^{*}_{s0}$ and $B_{s1}$, as hadronic molecules are revisited. This is necessary, since the $B^{*}_{s0}$ and $B_{s1}$ masses used in Eur. Phys. J. A 50 (2014) 149 were too small, in conflict with the heavy quark flavour symmetry. Furthermore, not all isospin breaking contributions were considered. We here present a method to restore heavy quark flavour symmetry, correcting the masses of $B^{*}_{s0}$ and $B_{s1}$, and include the complete isospin breaking contributions up to next-to-leading order. With this we provide updated hadronic decay widths for all of $D^{*}_{s0}$, $D_{s1}$, $B^{*}_{s0}$ and $B_{s1}$. Results for the partial widths of the radiative deays of $D_{s0}^*(2317)$ and $D_{s1}(2460)$ are also renewed in light of the much more precisely measured $D^{*+}$ width. We find that $B_sπ^0$ and $B_sγ$ are the preferred channels for searching for $B_{s0}^*$ and $B_{s1}$, respectively.

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arXiv2023

Neutron Scattering off One-Neutron Halo Nuclei in Halo Effective Field Theory

Neutron scattering off neutron halos can provide important information about the internal structure of nuclei close to the neutron drip line. In this work, we use halo effective field theory to study the $s$-wave scattering of a neutron and the spin-parity $J^P=\frac{1}{2}^+$ one-neutron halo nuclei $^{11}\rm Be$, $^{15}\rm C$, and $^{19}\rm C$ at leading order. In the $J=1$ channel, the only inputs to the Faddeev equations are their one-neutron separation energies. In the $J=0$ channel, the neutron-neutron scattering length and the two-neutron separation energies of $\rm ^{12}Be$, $\rm ^{16}C$ and $\rm ^{20}C$ enter as well. The numerical results show that the total $s$-wave cross sections in the $J=1$ channel at threshold are of the order of a few barns. In the $J=0$ channel, these cross sections are of the order of a few barns for $n$-$^{11}\rm Be$ and $n$-$^{19}\rm C$ scattering, and about 60 $\rm mb$ for the $n$-$^{15}\rm C$ scattering. The appearance of a pole in $p\cotδ$ close to zero in all three cases indicates the existence of a virtual Efimov state close to threshold in each of the $^{12}\rm Be$, $^{16}\rm C$, and $^{20}\rm C$ systems. Observation of this pole would confirm the presence of Efimov physics in halo nuclei. The dependence of the results on the neutron-core scattering length is also studied.

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arXiv2023

Reconciling experimental and lattice data of $Z_c(3900)$ in a $J/ψπ$-$D\bar{D}^*$ coupled-channel analysis

We study the $J/ψπ$ and $D\bar{D}^*$ coupled-channel system within a covariant framework. The $J/ψπ$ and $D\bar{D}^*$ invariant-mass distributions measured at 4.23~GeV and 4.26~GeV by BESIII and the finite-volume energy levels from recent lattice QCD simulations are simultaneously fitted. Phase shifts and inelasticities of the $J/ψπ$ and $D\bar{D}^*$ scattering are predicted using the resulting amplitudes. Poles corresponding to the $Z_c(3900)$ state are found in the complex energy plane and their couplings with $J/ψπ$ and $D\bar{D}^*$ are determined. Our results indicate that the current lattice data do not preclude the existence of a physical $Z_c(3900)$ state.

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arXiv2023

Radiative decays of the spin-$2$ partner of $X(3872)$

It has been generally expected that the $X(3872)$ has a spin-2 partner, $X_2$, with quantum numbers $J^{PC}=2^{++}$. In the hadronic molecular model, its mass was predicted to be below the $D^*\bar D^*$ threshold, and the new structure reported in the $γψ(2S)$ invariant mass distribution by the Belle Collaboration with mass $M= (4014.3 \pm 4.0 \pm 1.5)$ MeV and decay width $Γ= (4 \pm 11 \pm 6)$ MeV, with a global significance of 2.8 $σ$, is a nice candidate for it. We consider the radiative decay widths for the $X_{2}\to γψ$ with $ψ=J/ψ, ψ(2S)$ treating the $X_2$ as a $D^*\bar{D}^*$ shallow bound state, and estimate the events of $X_2$ in two-photon collisions that can be collected in the $γJ/ψ\toγ\ell^+\ell^-$ ($\ell=e,μ$) final states at Belle. Based on the upper limit for the ratio of decay widths of $X(3872)\to γψ(2S)$ and $X(3872)\to γJ/ψ$ measured by BESIII, we predict the similar ratio $Γ(X_2\to γψ(2S))/Γ(X_2\to γJ/ψ)$ to be smaller than $1.0$. We suggest searching for the $X_2$ signal in the $γJ/ψ$ invariant mass distribution via two-photon fusions. The results will lead to insights into both the $X(3872)$ and the new structure observed by Belle.

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arXiv2023

The case for an EIC Theory Alliance: Theoretical Challenges of the EIC

We outline the physics opportunities provided by the Electron Ion Collider (EIC). These include the study of the parton structure of the nucleon and nuclei, the onset of gluon saturation, the production of jets and heavy flavor, hadron spectroscopy and tests of fundamental symmetries. We review the present status and future challenges in EIC theory that have to be addressed in order to realize this ambitious and impactful physics program, including how to engage a diverse and inclusive workforce. In order to address these many-fold challenges, we propose a coordinated effort involving theory groups with differing expertise is needed. We discuss the scientific goals and scope of such an EIC Theory Alliance.

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arXiv2023

Isospin-conserving hadronic decay of the ${D_{s1}(2460)}$ into ${D_sπ^+π^-}$

The internal structure of the charm-strange mesons $D_{s0}^*(2317)$ and $D_{s1}(2460)$ are subject of intensive studies. Their widths are small because they decay dominantly through isospin-breaking hadronic channels $D_{s0}^*(2317)^+\to D_s^+π^0$ and $D_{s1}(2460)^+\to D_s^{*+}π^0$. The $D_{s1}(2460)$ can also decay into the hadronic final states $D_s^+ππ$, conserving isospin. In that case there is, however, a strong suppression from phase space. We study the transition $D_{s1}(2460)^+\to D_s^+π^+π^-$ in the scenario that the $D_{s1}(2460)$ is a $D^*K$ hadronic molecule. The $ππ$ final state interaction is taken into account through dispersion relations. We find that the ratio of the partial widths of the $Γ(D_{s1}(2460)^+\to D_s^+π^+π^-)/Γ(D_{s1}(2460)^+\to D_s^{*+}π^0)$ obtained in the molecular picture is consistent with the existing experimental measurement. More interestingly, we demonstrate that the $π^+π^-$ invariant mass distribution shows a double bump structure, which can be used to disentangle the hadronic molecular picture from the compact state picture for the $D_{s1}(2460)^+$. Predictions on the $B_{s1}^0\to B_s^0π^+π^-$ are also made.

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arXiv2023

Hadronic decays of the heavy-quark-spin molecular partner of $T_{cc}^+$

Starting from the hypothesis that the $T_{cc}^+$ discovered at LHCb is a $D^{\ast+} D^0/D^{\ast 0}D^+$ hadronic molecule, we consider the partial width of its heavy quark spin partner, the $T_{cc}^{\ast +}$ as a $D^{\ast +} D^{\ast 0}$ shallow bound state, decaying into the $D^{\ast}Dπ$ final states including the contributions of the $D^{\ast} D$ and $D^{\ast} π$ final state interaction by using a nonrelativistic effective field theory. Because of the existence of the $T_{cc}^+$ pole, the $I=0$ $D^{\ast} D$ rescattering can give a sizeable correction up to about $40\%$ to the decay widths considering only the tree diagrams, and the $D^{\ast} π$ rescattering correction is about $10\%$. The four-body partial widths of the $T_{cc}^{*+}$ into $D Dππ$ are also explicitly calculated, and we find that the interference effect between different intermediate $D^*Dπ$ states is small. The total width of the $T_{cc}^{*+}$ is predicted to be about 41 keV.

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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.

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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 $K\bar Kππ$.

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arXiv2023

Chromopolarizabilities of fully-heavy baryons

We compute the chromopolarizabilities of the fully heavy baryons $Ω_{QQQ'}$ ($Q,Q'=b,c$) in the framework of potential nonrelativistic quantum chromodynamics. At leading order, the fully heavy hadrons are considered as ground chromo-Coulombic bound states. We find that the chromopolarizability $β_Ω$ of a fully heavy baryon $QQQ$ is 2.6 times the chromopolarizability $β_ψ$ of the quarkonium $\bar{Q}Q$ with the same heavy quark flavor $Q$. This result is accurate up to the correction of the order 0.3 for $Q=b$ and provides an order-of-magnitude estimate for $Q=c$. We discuss the dependence of the ratio $β_Ω/β_ψ$ on the heavy quark mass $m_Q$ and the strong coupling constant $α_s$ as well as on the ratio of the masses $m_{Q'}/m_Q$, in the case not all quarks in the baryon are identical. Since the chromopolarizability of heavy hadrons defines the strength of their interaction at low energies mediated by soft gluons, which at long range hadronize into pairs of pions and kaons, our findings argue in favor of the existence of near-threshold states composed of pairs of fully heavy baryons.

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arXiv2023

Three-body coupled channel framework for two-neutron halo nuclei

We study the Borromean nuclei formed by a core nucleus and two neutrons in a nonrelativistic effective field theory formalism considering both neutron-neutron and neutron-core interactions. We provide formulae of the charge and matter radii, and successfully reproduce the universal relation proposed by Hongo and Son based on the approximation of an infinite neutron-neutron scattering length and neglecting the neutron-core scattering. Once the realistic finite neutron-neutron and neutron-core scattering lengths are used, the charge and matter radii are influenced by the neutron-core channel in a growingly relevant manner. We obtain a relation among the binding energy of the three-body Borromean system, the ratio between charge and matter radii, and the ratio between the neutron-neutron and core-neutron scattering lengths. We find that the two-neutron separation energy for $^{22}$C needs to be $\lesssim 2$ keV in order to be consistent with the experimental constraints of the matter radius of $^{22}$C and the $^{20}{\rm C}\,n$ $S$-wave scattering length.

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arXiv2022

Semi-inclusive electroproduction of hidden-charm and double-charm hadronic molecules

The semi-inclusive electroproduction of exotic hadrons, including the $T_{cc}$, $P_{cs}$, and hidden-charm baryon-antibaryon states, is explored under the assumption that they are $S$-wave hadronic molecules of a pair of charmed hadrons. We employ the Monte Carlo event generator Pythia to produce the hadron pairs and then bind them together to form hadronic molecules. With the use of such a production mechanism, the semi-inclusive electroproduction rates are estimated at the order-of-magnitude level. Our results indicate that a larger number of $P_{cs}$ states and $Λ_c\barΛ_c$ molecules can be produced at the proposed electron-ion colliders in China (EicC) and in the US (EIC). The results also suggest that the $T_{cc}$ states and other hidden-charm baryon-antibaryon states can be searched for at EIC. Besides, the potential 24-GeV upgrade of the Continuous Beam Accelerator Facility at the Thomas Jefferson National Accelerator Facility can play an important role in the search for the hidden-charm tetraquark and pentaquark states due to its high luminosity.

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arXiv2022

Establishing the heavy quark spin and light flavor molecular multiplets of the $X(3872)$, $Z_c(3900)$ and $X(3960)$

Recently, the LHCb Collaboration reported a near-threshold enhancement, $X(3960)$, in the $D_s^+D_s^-$ invariant mass distribution. We show that the data can be well described by either a bound or a virtual state below the $D_s^+D_s^-$ threshold. The mass given by the pole position is $(3928\pm3)$ MeV. Using this mass and the existing information on the $X(3872)$ and $Z_c(3900)$ resonances, a complete spectrum of the $S$-wave hadronic molecules formed by a pair of ground state charmed and anticharmed mesons is established. Thus, pole positions of the partners of the $X(3872)$, $Z_c(3900)$ and the newly observed $D_s^+D_s^-$ state are predicted. Calculations have been carried out at the leading order of nonrelativistic effective field theory and considering both heavy quark spin and light flavor SU(3) symmetries, though conservative errors from the breaking of these symmetries are provided.

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