arXiv subjects

Xiang-Kun Dong

Publications and source records attributed to Xiang-Kun Dong.

At least 19 recordsLinked to original sources

arXiv2026

Precise determination of the properties of $X(3872)$ and of its isovector partner $W_{c1}$

We perform a simultaneous fit to BESIII data on $e^+e^-\to γ(D^0{\bar{D}^{0}}π^0/J/ψπ^+π^-)$ and LHCb data on $B^+\to K^+(J/ψπ^+π^-)$ to precisely determine the properties of the $X(3872)$, with full consideration of three-body effects from $D^*\to Dπ$ decay, respecting both analyticity and unitarity. The $X(3872)$ is determined to be a quasi-bound state with a significance of $2.7\,σ$, representing the most precise determination to date. Its pole is located at $\left(-160^{+57}_{-74}-125^{+23}_{-38}\,i\right) \rm keV$, relative to the nominal $D^0\bar{D}^{*0}$ threshold. Moreover, we confirm the presence of an isovector partner state, $W_{c1}$. It is found as a virtual state at $\left(3.1\pm0.7+ 1.3^{+1.9}_{-0.6}\,i\right)\ \rm MeV$ relative to the $D^+ D^{*-}$ threshold on an unphysical Riemann sheet, strongly supporting a molecular nature of both $X(3872)$ and $W_{c1}$. As a highly nontrivial prediction we show that the $W_{c1}$ leads to nontrivial lineshapes around 3.88 GeV in $B^0\to K^0 X(3872)\to K^0 D^0\bar D^0π^0$ and $K^0J/ψπ^+π^-$ -- thus the scheme presented here can be tested further by improved measurements.

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arXiv2026

Vector charmonium(-like) states in the energy range of 4.1-4.6 GeV

The spectrum of vector charmonium(-like) states in the 4.1\dash4.6~GeV energy region exhibits a long-standing tension between inclusive and exclusive measurements. While the inclusive $R$-value indicates only conventional vector charmonia such as $ψ(4160)$ and $ψ(4415)$, exclusive $e^+e^-$ cross sections reveal additional structures whose parameters strongly depend on the observed final states when fitted with Breit--Wigner functions. This puzzling pattern suggests that coupled-channel and threshold effects play an essential role. In this work, we develop a unified coupled-channel framework for the $1^{--}$ resonances in this energy region. The framework incorporates the $S$-wave open-charm channels $D\bar{D}_1$, $D^*\bar{D}_1$, and $D^*\bar{D}_2^*$ constrained by heavy-quark spin symmetry, optional bare poles associated with $ψ(4160)$ and $ψ(4415)$, and final-state interactions in the $Z_c$ channels. We perform simultaneous fits to the BESIII cross sections for $e^+e^-\to J/ψπ^+π^-$, $h_cπ^+π^-$, $D\bar{D}^*π$, $D^*\bar{D}^*π$, $J/ψη$, and $χ_{c0}ω$, together with invariant-mass distributions exhibiting the $Z_c(3900)$ and $Z_c(4020)$ structures. The benchmark models differ in the number of bare seed states and the fitting strategy. We show that even the purely dynamical scheme without bare charmonia captures the gross features of the analyzed distributions. The inclusion of bare compact states improves the fit quality but does not change the conclusion that the measured line shapes can be understood in terms of strong coupled-channel effects with dynamically generated poles. We also discuss possible heavy-quark spin partners of the exotic $1^{--}$ states.

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arXiv2026

Amplified Isospin Breaking from Coupled-Channel Dynamics Near Threshold

We identify the dynamical origin of amplified isospin breaking in near-threshold states. Using a pole-residue-based measure defined directly from the pole couplings, rather than from decay observables that are also affected by different final-state kinematics, we show that threshold proximity of the pole alone is insufficient: large isospin breaking requires a sizable interaction in the companion isospin channel. Applied to the $X(3872)$, the observed large isospin breaking points to a nearby partner pole, $W_{c1}$, as predicted in previous studies. In addition, we find that the $W_{c1}$ pole, which predominantly affects the line shapes near the charged threshold in the physical case, does not evolve into the pure $I=1$ eigenstate in the isospin limit; instead, that eigenstate is continuously connected to a more distant shadow pole.

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arXiv2026

Decoding the structure near the $π^+π^-$ mass threshold in $ψ(3686) \rightarrow J/ψπ^+π^-$ decays

In light of recent high-precision data taken by the BESIII Collaboration, we reconsider the dipion transition $ψ(3686) \rightarrow J/ψπ^+π^-$. The strong pion-pion final-state interactions are taken into account model-independently by using dispersion theory. We find that we can reproduce the substructure near the $π^+π^-$ threshold observed experimentally without introducing an extra resonance state. While a helicity-flip amplitude plays an important role for the formation of the dip in the invariant-mass distribution, the virtual exchange of the charmoniumlike exotic $Z_c(3900)$ state improves the fit quality only slightly.

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arXiv2025

Deciphering the mechanism of $J/ψ$-nucleon scattering

The low-energy $J/ψN$ scattering is important for various reasons: it is related to the hidden-charm $P_c$ pentaquark states, provides insights into the role of gluons in nucleon structures, and is relevant to the $J/ψ$ properties in nuclear medium. The scattering can happen through two distinct mechanisms: the coupled-channel mechanism via open-charm meson-baryon intermediate states, and the soft-gluon exchange mechanism. We investigate the $J/ψN$ $S$-wave scattering length through both mechanisms, and find that the soft-gluon exchange mechanism leads to a scattering length at least one order of magnitude larger than that from the coupled-channel mechanism and thus is the predominant one. The findings can be verified by lattice calculations and will enhance our understanding of the scattering processes breaking the Okubo-Zweig-Iizuka rule.

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arXiv2025

Role of the short-range dynamics in the formation of $D^{()}\bar D^{()}/B^{()}\bar B^{()}$ hadronic molecules

We investigate potential hadronic molecular states in the $D^{(*)}\bar D^{(*)}$ and $B^{(*)}\bar B^{*}$ systems using light meson exchange interactions. Our analysis focuses on coupled-channel systems with spin-parity quantum numbers $J^{PC}=0^{++}$, $1^{+\pm}$ and $2^{++}$, examining how the $δ(r)$ potential affects states near threshold. Using coupled-channel analysis, we reproduce the $X(3872)$ mass with a given cutoff for the $(I)J^{PC}=(0)1^{++}$ state, finding a minimal impact from the $δ(r)$ term. At this cutoff, both the $(0)0^{++}$ state near the $D\bar D$ threshold and the $(0)1^{+-}$ state near the $D\bar D^*$ threshold show less sensitivity to the $δ(r)$ term compared to the three states-$(0)0^{++}$, $(0)1^{+-}$, and $(0)2^{++}$-near the $D^*\bar D^*$ threshold. As anticipated, the $B^{(*)}\bar B^{*}$ systems exhibit similar behavior but with stronger binding due to their larger reduced mass. These findings suggest promising directions for future experimental searches, particularly in the isoscalar sector, which could substantially advance our understanding of exotic tetraquark states.

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arXiv2025

The $J/ψ$-nucleon interaction mechanism: A theoretical study based on scattering length

The low-energy $J/ψN$ scattering is of significant importance for various reasons. It is deeply interconnected with the hidden-charm $P_c$ pentaquark states, provides insights into the role of gluons in nucleon structures, and is pertinent to the properties of $J/ψ$ in nuclear medium. The scattering can occur through two distinct mechanisms: the coupled-channel mechanism involving open-charm meson-baryon intermediate states $Λ_c \bar D^{(*)}$ and $ Σ_c^{(*)}\bar D^{(*)}$, and the soft-gluon exchange mechanism. In this study, we investigate the $S$-wave $J/ψN$ scattering length arising from both mechanisms. Our findings indicate that both mechanisms lead to attractive interactions, yielding scattering lengths of $[-10, -0.1] \times 10^{-3}$ fm for the coupled-channel mechanism and $<-0.16$ fm for the soft-gluon exchange mechanism, respectively. Notably, the soft-gluon exchange mechanism produces a scattering length that is at least one order of magnitude larger than that from the coupled-channel mechanism, indicating its predominance. These findings can be corroborated through lattice calculations and will enhance our understanding of scattering processes that violate the Okubo-Zweig-Iizuka rule.

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arXiv2024

Dispersive analysis of the isospin breaking in the $X(3872)~\to~J/ψπ^+π^-$ and $X(3872)~\to~J/ψπ^+π^0π^-$ decays

We analyze the latest LHCb data on the $π^+π^-$ spectrum in the isospin-violating $X(3872)\to J/ψπ^+π^-$ decay, based on dispersion theory to deal with the $ππ$ final state interactions. Additionally, the isospin breaking effects are properly introduced, allowing for a reliable and accurate extraction of the ratio, $R_X$, between the $X(3872)$ couplings to the $J/ψρ$ and $J/ψω$ channels from the data. We find very good agreement with the LHCb data for the whole range of the $π^+π^-$ invariant mass, and $R_X$ is determined to be {$0.26\pm 0.03$}. Using this value, we make predictions for the $π^+π^0π^-$ mass distribution in the $X(3872)\to J/ψπ^+π^0π^-$ process, which is currently accessible by the BESIII Collaboration, and update a prediction for the pole positions of the isovector partner states of the $X(3872)$, $W_{c1}$, with $I(J^{PC})=1(1^{++})$.

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arXiv2024

Predicting isovector charmonium-like states from X(3872) properties

Using chiral effective field theory, we predict that there must be isovector charmonium-like $D\bar D^*$ hadronic molecules with $J^{PC}=1^{++}$ denoted as $W_{c1}$. The inputs are the properties of the $X(3872)$, including its mass and the ratio of its branching fractions of decays into $J/ψρ^0$ and $J/ψω$. The predicted states are virtual state poles of the scattering matrix, pointing at a molecular nature of the $X(3872)$ as well as its spin partners. They should show up as either a mild cusp or dip at the $D\bar D^*$ thresholds, explaining why they are elusive in experiments. The so far negative observation also indicates that the $X(3872)$ is either a bound state with non-vanishing binding energy or a virtual state, only in these cases the $X(3872)$ signal dominates over that from the $W_{c1}^0$. The pole positions are $3881.2^{+0.8}_{-0.0}- i 1.6^{+0.7}_{-0.9}$ MeV for $W_{c1}^0$ on the fourth Riemann sheet of the $D^0\bar D^{*0}$-$D^+D^{*-}$ coupled-channel system, and $3866.9^{+4.6}_{-7.7}- i (0.07\pm0.01)$ MeV for $W_{c1}^\pm$ on the second Riemann sheet of the $(D\bar D^*)^\pm$ single-channel system. The findings imply that the peak in the $J/ψπ^+π^-$ invariant mass distribution is not purely from the $X(3872)$ but contains contributions from $W_{c1}^0$ predicted here. The states should have isovector heavy quark spin partners with $J^{PC}=0^{++}$, $2^{++}$ and $1^{+-}$, with the last one corresponding to $Z_c$. We suggest to search for the charged $0^{++}$, $1^{++}$ and $2^{++}$ states in $J/ψπ^\pm π^0$.

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arXiv2024

Interactions of the Pseudoscalar Meson Octet and the Baryon Decuplet in the Continuum and a Finite Volume

This study focuses on the interaction of the pseudoscalar meson octet and the baryon decuplet. In the continuum, it is observed that several $J^{P}=\frac32^-$ baryon resonances can be produced by the Weinberg-Tomozawa interaction in unitarized chiral perturbation theory, including the $N(1875)$, $Σ(1670)$, $Σ(1910)$, $Ξ(1820)$ and $Ω(2012)$. Among them, the $Ξ(1820)$ and $Σ(1670)$ may exhibit a potential two-pole structures. The unitarized chiral perturbation approach is then applied as the underlying theory to predict the energy levels of these systems in a finite volume. These energy levels are well described by the $K$-matrix parameterization constrained by flavor SU(3) symmetry. With the parameters from the best fits, the poles extracted from the $K$-matrix parameterization closely correspond to those derived from the underlying chiral effective field theory, as long as they are close to physical region and not significantly higher than the lowest relevant threshold.

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arXiv2024

Hints of the $J^{PC}=0^{--}$ and $1^{--}$ $K^*\bar K_1(1270)$ Molecules in the $J/ψ\toϕηη'$ Decay

The primary objective of this study is to investigate hadronic molecules of $K^*\bar K_1(1270)$ using a one-boson-exchange model, which incorporates exchanges of vector and pseudoscalar mesons in the $t$-channel, as well as the pion exchange in the $u$-channel. Additionally, careful consideration is given to the three-body effects resulting from the on-shell pion originating from $K_1(1270)\to K^*π$. Then the BESIII data of the $J/ψ\toϕηη'$ process is fitted using the $K^*\bar K_1(1270)$ scattering amplitude with $J^{PC}=0^{--}$ or $1^{--}$. The analysis reveals that both the $J^{PC}=0^{--}$ and $1^{--}$ assumptions for $K^*\bar K_1(1270)$ scattering provide good descriptions of the data, with similar fit qualities. Notably, the parameters obtained from the best fits indicate the existence of $K^*\bar K_1(1270)$ bound states, denoted by $ϕ(2100)$ and $ϕ_0(2100)$ for the $1^{--}$ and $0^{--}$ states, respectively. The current experimental data, including the $η$ polar angular distribution, cannot distinguish which $K^*\bar K_1(1270)$ bound state contributes to the $J/ψ\toϕηη'$ process, or if both are involved. Therefore, we propose further explorations of this process, as well as other processes, in upcoming experiments with many more $J/ψ$ events to disentangle the different possibilities.

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arXiv2024

Possible $Σ_c^* \barΣ$ molecular states

We investigate the possibility of deuteron-like $Σ_c^*\barΣ$ bound states within the one-boson-exchange model and systematically analyze the effects of the contact-range $δ^{3}(\vec{r}\,)$ potential, the tensor term from the vector-meson exchange, and nonlocal potentials due to the dependence on the sum of the initial and final state center-of-mass momenta. We find that the pion-exchange potential including the $δ^{3}(\vec{r}\,)$ term and the tensor term of the $ρ$-exchange potential exhibit comparable magnitudes but opposite signs for any $S$-wave baryon-antibaryon systems. For the $Σ_c^*\barΣ$ system, it is most likely to form bound states with mass around 3.7 GeV in the $I(J^P)=0(2^-)$ and $1(2^-)$ channels.

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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

Spin-orbit amplitudes for decays with arbitrary spin

In this paper, we propose a method to construct the decay amplitudes in the orbital ($L$) and spin ($S$) coupling scheme for particles with arbitrary spins. For the $1\to 2$ decay with only massive particles involved, the angular dependence is completely encoded in the angular momentum part, and the spins of daughter particles are coupled in the rest frame of the mother particle, which contributes only a constant factor. For the sequential decay, the total amplitude is constructed by the two $1\to2$ amplitudes evaluated in the rest frame of their own mother particles, and then they are transformed to the common frame, usually chosen as the laboratory frame, by certain Lorentz transformations. In this way, it is easy to add the amplitudes of possible different decay chains coherently. If massless particles show up in the final states, the polarizations are expressed in helicity basis and the amplitudes are modified correspondingly.

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arXiv2023

Molecular states in $D_s^{()+}Ξ_c^{(',)}$ systems

The possible hadronic molecules in $D_s^{(*)+}Ξ_c^{(',*)}$ systems with $J^P=1/2^-,3/2^-$ and $5/2^-$ are investigated with interactions described by light meson exchanges. By varying the cutoff in a phenomenologically reasonable range of $1\sim2.5$ GeV, we find ten near-threshold (bound or virtual) states in the single-channel case. After introducing the coupled-channel dynamics of $D_s^{+}Ξ_c$-$D_s^{+}Ξ_c^{'}$-$D_s^{*+}Ξ_c$-$D_s^{+}Ξ_c^{*}$-$D_s^{*+}Ξ_c^{'}$-$D_s^{*+}Ξ_c^{*}$ systems, these states, except those below the lowest channels in each $J^{P}$ sector, move into the complex energy plane and become resonances in the mass range of $4.43\sim4.76$ GeV. Their spin-parities and nearby thresholds are $1/2^-(D_s^{+}Ξ_c)$, $1/2^-(D_s^{+}Ξ_c^{'})$, $1/2^-(D_s^{*+}Ξ_c)$,$1/2^-(D_s^{*+}Ξ_c^{'})$, $1/2^-(D_s^{*+}Ξ_c^{*})$ , $3/2^-(D_s^{*+}Ξ_c)$, $3/2^-(D_s^{+}Ξ_c)$, $3/2^-(D_s^{*+}Ξ_c^{'})$, $3/2^-(D_s^{*+}Ξ_c^{*})$, and $5/2^-(D_s^{*+}Ξ_c^{*})$. The impacts of the $δ(r)$-term in the one-boson-exchange model on these states are presented. Setting $Λ=1.5$ GeV as an illustrative value, it is found that $1/2^-(D_s^{+}Ξ_c)$ is a stable bound state (becoming unstable if turning on the coupling to lower channels), $1/2^-(D_s^{*+}Ξ_c)$ and $3/2^-(D_s^{*+}Ξ_c)$ are physical resonances in both cases of including or excluding the $δ(r)$-term, while the other seven states are physical resonances or ``virtual-state-like" poles near thresholds, depending on including the $δ(r)$-term or not. In addition, the partial decay widths of the physical resonances are provided. These double-charm hidden-strangeness pentaquark states, as the partners of experimentally observed $P_c$ and $P_{cs}$ states, can be searched for in the $D^{(*)}Λ_c$ final states in future.

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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

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

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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