arXiv subjects

Si-Qiang Luo

Publications and source records attributed to Si-Qiang Luo.

At least 19 recordsLinked to original sources

arXiv2026

Truncation of the Radial Ladder in Heavy Quarkonia

A fundamental open question in hadron spectroscopy is whether the radial excitation ladder of quarkonia truncates at a finite level---a possibility that would challenge the conventional quark-antiquark bound-state picture and offer decisive clues to the nonperturbative strong interaction. Taking advantage of the newly observed high-mass hadronic states, we address this issue by solving a screened Godfrey--Isgur Hamiltonian for charmonium and bottomonium using the Gaussian expansion method. The calculated spectra saturate at $4.74\,\mathrm{GeV}$ ($c\bar{c}$) and $11.67\,\mathrm{GeV}$ ($b\bar{b}$), while root-mean-square radii grow to $\sim10\,\mathrm{fm}$---an order of magnitude above the confinement scale---where adjacent mass gaps drop below $10\,\mathrm{MeV}$. Combining a threshold-based mass-gap criterion, defined by the onset of mass--radius decoupling, with additional diagnostics, we locate the operational upper radial limits at $n\approx8$--$10$ for charmonium and $n\approx12$--$13$ for bottomonium. Beyond these limits, the conventional $q\bar{q}$ description ceases to apply. This work provides the first quantitative determination of these upper limits, and the proposed criterion is directly testable with forthcoming high-statistics data from BESIII, Belle II, and LHCb.

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arXiv2026

Systematic exploration of triply heavy tetraquarks: spectroscopic and decay characteristics

While hidden, singly, doubly, and fully heavy tetraquark states have been experimentally observed, triply heavy tetraquark states remain experimentally unconfirmed. We systematically investigate the spectroscopic and decay properties of four triply heavy-flavor tetraquark systems ($cc\bar{c}\bar{n}$, $cc\bar{c}\bar{s}$, $bb\bar{b}\bar{n}$, $bb\bar{b}\bar{s}$; $n=u,d$) based on the nonrelativistic quark model. Using an effective Hamiltonian, we employ the Gaussian expansion method to solve the four-body Schr\"{o}dinger equation and incorporate the effect of color-spin configuration mixing. Results show both $cc\bar{c}\bar{q}$ and $bb\bar{b}\bar{q}$ systems have two $J^{P}=0^{+}$, three $J^{P}=1^{+}$, and one $J^{P}=2^{+}$ states, with ground-state masses of 5.2-5.5 GeV and 15.0-15.3 GeV, respectively. Root-mean-square radius analysis supports compact tetraquark configurations. All states are unstable, with rearrangement strong decays dominant and negligible radiative decays. Narrow resonances (e.g., $T_{c^{2}\bar{c}\bar{s}}(5360,0^{+})$, $T_{b^{2}\bar{b}\bar{n}}(15148,2^{+})$) arise from Feynman amplitude cancellation. We propose experimental searches in $J/\psi D^{*}_{s}$/ $\eta_{c}D_{s}$ (5.3-5.4 GeV) and $\Upsilon B^{*}$ (15.1-15.2 GeV) channels, providing key guidance for triply heavy tetraquark identification.

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arXiv2026

Unquenched Charmonium and Beyond

The year 2024 marked the 50th anniversary of the discovery of the $J/\psi$ particle, which unveiled the charm quark and the charmonium spectrum, instigating the "November Revolution" in particle physics. This discovery catalyzed the development of quenched potential models, most notably the Cornell model, which provided a foundational quantitative description of the hadronic spectrum. However, the landscape of hadron spectroscopy has been profoundly transformed since the turn of the 21st century with the observation of numerous charmonium-like states, such as $X(3872)$, which exhibit properties starkly at odds with quenched model predictions. These discrepancies, exemplified by the "$X(3872)$ low-mass puzzle" and the "$Y$ problem" associated with vector states like $Y(4260)$, underscore the critical limitations of the quenched approximation and signal the necessity for a new theoretical paradigm. This review synthesizes recent advances in hadronic spectroscopy, arguing that the unquenched picture, which incorporates coupled-channel effects such as hadronic loops, is essential for a unified description of these new states and associated anomalies. We demonstrate how unquenched effects provide compelling solutions to long-standing puzzles in charmonium decays (e.g., the "$\rho\pi$ puzzle" and anomalous dipion transitions), predict and explain the existence of exotic charged states like $Z_c(3900)$ and $Z_b(10610)$ via mechanisms such as Initial Single Pion Emission, and offer a framework for understanding interactions between charmonia and with nucleons. Furthermore, we emphasize the universality of unquenched effects, extending their application to bottomonium and light-flavor sectors. As experimental precision continues to improve, we advocate for the systematic development of unquenched hadronic spectroscopy.

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arXiv2026

Assessing the validity of the Born-Oppenheimer approximation in potential models for doubly heavy hadrons

The Born-Oppenheimer approximation is widely used to investigate the properties of hydrogen-like systems and doubly heavy hadrons. However, the extent to which this approximation captures the features of such systems within potential models remains an open question. In this work, we adopt the results obtained with the Gaussian expansion method as a benchmark to assess the validity of the Born-Oppenheimer approximation within potential models for hadronic systems. We also investigate the dependence of the Born-Oppenheimer approximation results on the choice of trial wave functions. A comprehensive study of the Born-Oppenheimer approximation is carried out by performing calculations using Slater-type functions and Gaussian-type functions as trial wave functions, and by comparing the resulting predictions with those obtained from the Gaussian expansion method. We find that the calculations performed within the Born-Oppenheimer approximation are close to those obtained with the Gaussian expansion method when the heavy-quark mass is relatively small. However, as the heavy-quark mass increases, calculations employing Slater-type functions yield larger values than those from the Gaussian expansion method, whereas those using Gaussian-type functions lead to smaller ones. The use of Slater-type functions generally leads to an enhanced binding energy. The underestimation observed in Born-Oppenheimer approximation calculations with Gaussian-type functions primarily stems from the neglect of non-adiabatic corrections. This comparative study provides deeper insight into the structure of doubly heavy hadrons and helps clarify the applicability and limitations of the Born-Oppenheimer treatment within potential models.

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arXiv2025

Is the $3S$-$2D$ mixing strong for the charmonia $ψ(4040)$ and $ψ(4160)$?

In this work, we revisit the $3S$-$2D$ mixing scheme for the charmonia $ψ(4040)$ and $ψ(4160)$. We introduce a coupled-channel mechanism-distinct from the tensor-force contribution in potential models, which alone is insufficient to induce significant mixing-to describe the mixing between these states. Our analysis yields mixing angles of $θ_1=7^\circ$ and $θ_2=10^\circ$, inconsistent with the larger angle inferred from experimental data, such as the dilectronic widths of the $ψ(4040)$ and $ψ(4160)$. We discuss possible origins of this discrepancy and emphasize the need for future experiments to resolve it. Precise measurements of the resonance parameters and dilectronic decay widths, via both inclusive and exclusive processes, will be crucial in clarifying this issue.

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arXiv2025

Predicting charmed-strange molecular tetraquarks with $K^{(*)}$ and $T$-doublet charmed or anticharmed meson

In this work, we first present a systematic investigation of the $T_{\bar{c}\bar{s}}$-type charmed-strange molecular tetraquark candidates composed of a $K^{(*)}$ meson and a $T$-doublet anticharmed meson using the one-boson-exchange model, which exhibit exotic flavor content $\bar{c}\bar{s} q q$. Our results suggest that the $K^* \bar D_1$ states with $I(J^P)=0(0^-,\,1^-)$ and the $K^* \bar D_2^*$ states with $I(J^P)=0(1^-,\,2^-)$ represent the most promising candidates of the $T_{\bar{c}\bar{s}}$-type charmed-strange molecular tetraquarks, while the coupled $K \bar D_1 / K^* \bar D_1 / K^* \bar D_2^*$ system with $I(J^P)=0(1^-)$ and the coupled $K \bar D_2^* / K^* \bar D_1 / K^* \bar D_2^*$ system with $I(J^P)=0(2^-)$ can only be regarded as the possible candidates of the $T_{\bar{c}\bar{s}}$-type charmed-strange molecular tetraquarks. We further extend our analysis to the $K^{(*)} {D}_1/K^{(*)} {D}_2^*$ systems, where our results suggest a series of $T_{c \bar s}$-type charmed-strange molecular tetraquark candidates. These findings provide a comprehensive picture of the molecular spectrum in the charmed-strange tetraquark sector composed of $S$-wave kaons and (anti-)charmed mesons in the $T$-doublet and can be tested in future experimental studies.

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arXiv2025

Spectroscopic properties of $1F$-wave singly bottom baryons

This study investigates the mass spectra and decay behaviors of the experimentally unobserved $1F$-wave singly bottom baryons. Calculating their mass spectra could provide crucial guidance for determining their spectroscopic positions. Additionally, by analyzing their decay properties, we could predict the important decay channels, which are essential for experimental searches and quantum number assignments. Our calculations aim to support ongoing experimental and theoretical efforts in singly bottom baryon spectroscopy.

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arXiv2025

Triply heavy baryon spectroscopy revisited

We present a comprehensive study of triply heavy baryons ($Ω_{ccc}$, $Ω_{bbb}$, $Ω_{bcc}$, and $Ω_{bbc}$) within the nonrelativistic quark model, employing the Gaussian expansion method to calculate mass spectra up to $D$-wave states. Our analysis represents the most complete treatment to date for this model, incorporating full angular momentum mixing effects. While our predictions for low-lying states agree well with lattice quantum chromodynamics (QCD) results, we find systematically lower masses for excited states compared to lattice calculations. Using the obtained wave functions, we estimate radiative decay widths up to $1D$ states, revealing significant differences from previous theoretical work. Additionally, we identify and resolve several misconceptions in prior treatments of triply heavy baryon spectroscopy, particularly symmetry constraint and wave function construction in three-quark systems. These results provide crucial information for future experimental searches and theoretical investigations of triply heavy baryon systems.

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arXiv2025

Doubly charmed hexaquarks in the diquark picture

We investigate doubly charmed hexaquark states within the diquark picture, by employing the constituent quark model and the quark-interchange model as our theoretical frameworks. Using the Gaussian expansion method, we systematically study these states, with calculating various properties such as mass spectra, internal contributions of each Hamiltonian component, root-mean-square radii, and two-body strong decay widths. Our analysis of the mass spectra reveals no stable state in this system. Furthermore, the root-mean-square radii suggest that the doubly charmed hexaquark states exhibit a compact configuration. By examining the decay widths, we identify potentially detectable states and their primary decay channels within each subsystem. Despite the large decay phase space, we still find narrow states with total widths of less than 10 MeV. This study provides a theoretical foundation for understanding the structures and interactions of doubly charmed hexaquark states and offers valuable insights for future experimental searches.

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arXiv2025

Investigating topped hadrons to probe the boundaries of the potential model

Inspired by the recent discovery of a pseudoscalar enhancement structure near the $t\bar{t}$ threshold reported by the CMS and ATLAS Collaborations, this work investigates the mass spectra of single topped hadrons-including both topped mesons and topped baryons-based on a relativistic potential model. Using the same parameters obtained from the fit to mesons and baryons, we provide predictions for the mass spectra of ground and low-lying orbitally excited single topped mesons and baryons. In addition, we point out that the precise measurement of the $t\bar{t}$ mass could test the limitation of the potential model. Given the extremely large mass of the topped quark, we discuss spectroscopic properties of topped hadrons in the approximation of an ideal heavy-quark limit.

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arXiv2025

Identifying triple-strangeness $Ω$ hyperons in light of recent experimental results

In this work, we systematically calculate the mass spectra and decay widths of $Ω$ baryons with $N\leq3$, where $N=2n_ρ+2n_λ+l_ρ+l_λ$ is the shell of the three-body harmonic oscillator. In our scheme, the newly observed $Ω(2109)$ is identified as a $N=2$ candidate, with its quantum numbers tentatively assigned as $Ω(2S,3/2^+)$. However, the experimentally measured mass exhibits a deviation of approximately 50 MeV below the theoretical predictions. The possible reason for this deviation, along with the suggestion for experiments, are discussed in this paper. Additionally, we give possible assignments of $Ω(2012)^-$, $Ω(2250)^-$, $Ω(2380)^-$, and $Ω(2470)^-$. Furthermore, we calculate the masses and widths of other missing $Ω$ states, which could provide valuable clues for experimental searches aimed at discovering these states.

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arXiv2025

Coupled-channel study of $4S$-$3D$ mixing dynamics in $ψ(4220)$ and $ψ(4380)$

Among charmoniumlike $XYZ$ states, the $ψ(4220)$ and $ψ(4380)$ states have emerged as key candidates for exploring the charmonium spectrum. In this work, we propose a $4S$-$3D$ charmonium mixing scheme for the $ψ(4220)$ and $ψ(4380)$, induced by coupled-channel effects. By constructing a coupled-channel model, we identify the dynamical mechanism responsible for the large mixing angle observed in previous studies, which cannot be explained by conventional potential models alone. Our analysis reveals that the $DD_1$ channel significantly influences the lower state ($ψ(4220)$), while the $D^*D_1$ channel primarily affects the higher state ($ψ(4380)$). Furthermore, we investigate the two-body Okubo-Zweig-Iizuka (OZI)-allowed strong decay behaviors of these states, providing insights into their total widths. This study not only supports the $4S$-$3D$ mixing scheme but also offers a deeper understanding of the role of coupled channels in shaping the charmonium spectrum above 4 GeV. Our results align with experimental observations and provide a framework for interpreting future data on charmonium states.

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arXiv2025

Electromagnetic properties of possible triple-charm molecular hexaquarks

In this study, we investigate the radiative transitions of predicted triple-charm molecular hexaquarks, which play a significant role in understanding their overall spectroscopic properties. As experimentally measurable quantities, the radiative decay widths provide insights into the internal structures of these triple-charm molecular hexaquarks. Additionally, we calculate their corresponding magnetic moments, which, together with the radiative decay widths, offer a comprehensive picture of the electromagnetic properties of these exotic states. This information is valuable for guiding future experimental searches and advancing our understanding of these unique hadronic systems.

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arXiv2025

Scalar resonance contributions in the $D_{s1}(2460)^{+} \rightarrow D_{s}^{+}π^{+}π^{-}$ reaction

Inspired by the newly observed $T_{c\bar{s}}$ state in the $D_{s1}(2460)^{+} \rightarrow D_{s}^{+}π^{+}π^{-}$ reaction by the LHCb Collaboration, we investigate the amplitude of this decay to explore the origins and properties of the open-charm tetraquark state based on the final state interaction. The invariant mass distributions of $D_{s}^{+}π^{+}$ and $π^{+}π^{-}$ are well reproduced by the $S$-wave scattering amplitudes of the coupled channel systems $D_{s}π$ and $ππ$. However, neither the tree-level nor both the tree-level and $ππ$ coupled channel scattering contributions can describe the experimental data well, which indicates that the $D_{s}π$ coupled channel scattering is required. We find that the $T_{c\bar{s}}$ and $f_{0}(500)$ resonances are dynamically generated from the pseudoscalar-pseudoscalar meson interaction within the chiral unitary approach. In addition, we find the corresponding poles and also calculate the $S$-wave scattering length for the $DK$ channel, which is on the same scale as the result extracted from the experiment. We propose that the $T_{c\bar{s}}$ and $f_{0}(500)$ resonances in the $D_{s1}(2460)^{+} \rightarrow D_{s}^{+}π^{+}π^{-}$ reaction are hadronic molecular type particles.

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arXiv2025

Unveiling the Composition of the Single-Charm Molecular Pentaquarks: Insights from Radiative Decay and Magnetic Moment

In order to unravel the composition of the isoscalar $DN$, $D^*N$, $D_1N$, and $D_2^*N$ molecular pentaquarks, we carry out a systematic investigation of their M1 and E1 radiative decays and magnetic moment properties. Using the constituent quark model and taking into account the $S$-$D$ wave mixing effect and the coupled channel effect, our analysis yields numerical results indicating that the M1 and E1 radiative decays and the magnetic moment properties of these molecular pentaquarks provide some insights into their inner structures. These results can provide crucial clues for distinguishing their spin-parity quantum numbers and configurations in experimental studies. In addition, we highlight the importance of the electromagnetic properties as key observables for elucidating the inner structures of the observed $Λ_c^{+} (2940)$ and $Λ_c^{+} (2910)$. We hope that these findings can inspire our experimental colleagues to further explore the family of the single-charm molecular pentaquarks and to investigate the inner structures of the $Λ_c^{+} (2940)$ and $Λ_c^{+} (2910)$ in future studies.

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arXiv2024

Spectroscopic Properties of Double-Strangeness Molecular Tetraquarks

Inspired by recent advances in the study of the $K^{(*)} \bar K^{(*)}$ molecular tetraquarks and the $H$-dibaryon, we focus on the spectroscopic properties of the $\bar K^{(*)} \bar K^{(*)}$ systems, which exhibit exotic flavor quantum number of $ss\bar q \bar q$. A dynamical analysis is performed using the one-boson-exchange model to describe the effective interactions for these systems, accounting for both $S$-$D$ wave mixing and coupled-channel effects. By solving the coupled-channel Schr$\ddot{\rm o}$dinger equation, we identify the $I(J^P)=0(1^+)$ $\bar K \bar K^*$ and $I(J^P)=0(1^+)$ $\bar K^* \bar K^*$ states as the most likely candidates for double-strangeness molecular tetraquarks. Furthermore, we estimate their strong decay behaviors based on the effective Lagrangian approach, with several channels exhibiting considerable decay widths. Meanwhile, we investigate their magnetic moments and M1 radiative decay widths, shedding light on their inner structures, within the constituent quark model. Finally, we encourage experimentalists to focus on these predicted double-strangeness molecular tetraquark candidates, particularly in $B$ meson decays. Such efforts could pave the way for establishing the molecular tetraquark states in the light-quark sector.

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arXiv2024

Masses and radiative decay widths of the $D_{s0}^*(2317)$ and $D_{s1}^{\prime}(2460)$ and their bottom analogs

We study the mass spectra and radiative decays of $D_{s0}^*(2317)$ and $D_{s1}^{\prime}(2460)$ in an unquenched framework. In addition to coupled channel effects between the $c\bar{s}$ cores and $D^{(*)}K$ channels, $D^{(*)}K$-$D^{(*)}K$ self interactions are also considered in this work and we succeed to reproduce their mass spectra. Furthermore, we study the radiative decays of the $D_{s0}^*(2317)$ and $D_{s1}^{\prime}(2460)$ by simultaneously including the compound structures of conventional $c\bar{s}$ cores and $D^{(*)}K$ components. We also calculate their bottom analogs with heavy quark symmetry. Our study offers useful insights into the important unquenched effects in the formation of $D_{s0}^*(2317)$, $D_{s1}^{\prime}(2460)$ and the bottom counterparts.

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arXiv2024

Refining radiative decay studies in singly heavy baryons

In this work, we systematically study the radiative decays of singly heavy baryons, a crucial aspect of their spectroscopic behavior. To enhance the accuracy of our calculations, we utilize numerical spatial wave functions for the singly heavy baryons obtained through the Gaussian expansion method, which also yields their mass spectrum. As hadron spectroscopy enters an era of high precision, we believe our study of the radiative decays of singly heavy baryons will provide valuable insights for further exploration of these particles.

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