arXiv subjects

Wen-Xuan Zhang

Publications and source records attributed to Wen-Xuan Zhang.

15 recordsLinked to original sources

arXiv2026

Termination of the Radial Ladder in Mixed-Flavor Heavy Mesons

A fundamental open question in hadron spectroscopy is whether the radial excitation ladder of heavy mesons terminates at a finite level once confinement is screened by light-quark pair creation. We address this question for the mixed-flavor mesons $D_s$, $B_s$, and $B_c$ by solving a screened Godfrey--Isgur Hamiltonian with the Gaussian expansion method. The screening length is fixed by threshold-dependent string breaking analysis, and is matched to the charmonium and bottomonium anchors. The calculated spectra saturate at $3.36$, $6.78$, and $8.19~{\rm GeV}$ in $D_s$, $B_s$, and $B_c$ families, while the RMS radii grow by several fm and mass gaps fall below $10~{\rm MeV}$. Mass-radius decoupling places the end of the safe radial ladder at $n_{\mathrm{safe}}\approx 4$--$6$ for $D_s$, $5$--$7$ for $B_s$, and $9$--$11$ for $B_c$, so the ladder terminates first in $D_s$, then in $B_s$, and last in $B_c$. Above the limiting-mass windows, at $3.49$, $6.86$, and $8.24~{\rm GeV}$, states of the radial ladder cannot be discovered. This termination is directly testable with forthcoming high-statistics data from BESIII, Belle II, and LHCb.

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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

Mass relations in heavy hadrons from Jensen-like inequalities

We demonstrate that mass inequalities for hadrons with one or more heavy quarks arise primarily from the concavity of binding energies in the quark model, reflecting short-range Coulombic interactions and long-range confinement. Empirical two-body bindings $B_{i\bar{j}}$ are extracted from spin-averaged meson masses, ensuring model independence and direct use of experimental data. Fitting these as functions of reduced mass $μ_{ij}$ reveals a critical confinement scale of 1.34~fm where bindings turn positive. The concave $B(1/μ)$ justifies Jensen-like inequalities under flavor permutation, reproducing relations like $m_{x\bar{y}} > \frac{1}{2}(m_{x\bar{x}} + m_{y\bar{y}})$ and baryon analogs, including $m_{xyz} > \frac{1}{3}(m_{xxx} + m_{yyy} + m_{zzz})$. Hadron mass decomposition validates $ΔM_{\textrm{EXP}} \approx ΔB + ΔC$ with $σ\sim 2.07$~MeV for mesons and baryons. Promoting inequalities to equalities, we predict masses for unobserved heavy baryons (e.g., $M(Ω_{b}^{\ast})=6076.6\,$MeV, $M(Ξ_{cc}^{\ast})=3703.6\,$MeV and $M(Ω_{cc}^{\ast})=3802.4\,$MeV) and identify favored quark-exchange scattering channels.

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arXiv2026

Experimental Demonstration of Twin-Field Quantum Digital Signatures over 504 km

Digital signatures are one of the security cornerstones of the current information age. Compared with classical digital signatures based on computational complexity, quantum digital signatures (QDS) theoretically guarantee data integrity, authenticity, and non-repudiation by quantum mechanics, showing great potential for development in cryptography and thus attracting widespread attention. However, the performance of existing QDS systems are still limited in rate and distance. Here we report the first experimental demonstration of twin-field QDS (TF-QDS) using a GHz system. We achieve a maximum transmission distance of 504 km fiber spools for both single-bit and multi-bit schemes, surpassing all existing state-of-the-art QDS experiments more than 200 km. Furthermore, by combining the one-time universal hash method, we achieve a maximum signature rate of 21.1 times per second for a 1 Mbit file over fiber distances up to 302 km. In this work, the signature rates of both single-bit scheme and multi-bit scheme are more than two orders of magnitude higher than that of previous works at similar distance. Our work provides a new record for long-distance and high-rate QDS, representing a significant step in the development of QDS.

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arXiv2025

Prospects for compact hexaquarks under the limitation imposed by quark confinement

The limitation of flavor constituents for compact multiquarks is crucial for understanding the strong interaction at the low energy scale. Utilizing the MIT bag model that incorporates perturbative interactions and confinement energy $E_{\rm CON}$, we derive a critical bag radius $R_c=5.61\,$GeV$^{-1}$ from the condition $E_{\rm CON} < 0$ at zero temperature and zero baryon density, which aligns with the string-breaking distance of 1.2--1.4$\,$fm. Applying this framework to 6-, 7-, and 8-quark systems, we find the bag radii $R_0$ to be highly sensitive to relativistic effects from light quarks, leading to the exclusion of most heavy-light flavor configurations (e.g., $n^3\bar{c}^3$, $n^3\bar{n}\bar{c}^2$) due to positive $E_{\rm CON}$ and radii exceeding the critical radius. Color-spin wavefunctions are constructed using Young tableaux to evaluate interaction matrices and OZI-superallowed decays. Broad decay widths in fully heavy systems for OZI-superallowed modes could arise from wavefunction overlaps due to heavy flavor symmetry, suggesting possible narrow widths for $nnb\bar{b}\bar{b}\bar{b}$ and $nnn\bar{b}\bar{b}\bar{b}$ hexaquarks. This phenomenological approach provides insights into the limitations on multiquarks imposed by confinement. It recommends experimental searches at LHCb for these states.

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arXiv2025

Resonant Singly Heavy Pentaquarks in the MIT Bag Model: Mass Spectra and Strong Decays

Exploring the limits of color interactions in multiquark states is an important topic. Based on the bag confinement picture of hadrons, we find that for singly heavy pentaquarks, the bag confinement radius precisely falls within the range of color interaction limits provided by lattice QCD, approximately 1.17--1.29$\,\text{fm}$. This leads us to believe that singly heavy pentaquark states have the potential to form resonant states. Inspired by singly heavy baryons, we consider the mirror pentaquarks of singly heavy baryons. Furthermore, we adopt the MIT bag model, taking into account chromomagnetic and color-electric interactions between heavy and strange quarks, to calculate the mass spectrum of singly heavy pentaquarks configured as $qqqQ\bar{q}$ and analyze the stability of their S-wave two-body strong decays. We show that for the singly heavy pentaquark system, the masses are generally about $500\, \text{MeV}$ higher than the corresponding mirror baryon ground state masses, which is consistent with conclusions drawn from chiral methods. We also provide a mass mapping relationship between singly heavy pentaquarks and singly heavy baryons based on light quark flavor symmetry. The analysis of strong decays indicates that these singly heavy pentaquarks are unstable with respect to strong decays, which is consistent with our initial hypothesis.

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arXiv2025

Systematics of doubly heavy tetraquarks: nonstrange and strange

Masses, magnetic moments and color-spin structures of nonstrange and strange tetraquarks with two heavy quarks are systematically studied in QCD string picture with chromomagnetic interaction. Our mass computations combined with weak and radiative decays indicate that there are two doubly-heavy tetraquarks, the bottom-charmed tetraquark $T_{cb}(7173,01^+)^0$ and the doubly-bottom tetraquark $T_{bb}(10406,01^+)^-$, to be stable against the strong decay, having the lifetimes of $0.069$ fs and $326$ fs, respectively. Magnetic moments are also computed and found to be sensitive to chromomagnetic mixing of the color-spin configurations of these tetraquarks, being valuable probe to experimentally detect the nontrivial color configuration $6_{c}\otimes\bar{6}_{c}$.

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arXiv2025

Searching for compact pentaquark state within the bag model framework

The search for the compact limit of multi-quark states is a challenging issue. Within the framework of the MIT bag model, we propose an effective limit bag radius of $R_{c} = 5.615 \, \text{GeV}^{-1}$(or $1.11 \, \text{fm}$) for bound states . When the bag radius of a hadron falls below this value, the bag binding energy satisfies $E_{B} < 0$, indicating that the system has a compact intention. We consider various combinations of different numbers and ratios of heavy and light quarks, indicating that the bag radius of hadrons depending on the number of quarks is suppressed by the presence of heavy quarks. Focusing on five-quark combinations, we find that the average bag radius of $nncc\bar{c}$ is below the threshold $R_{c}$. We take into account color-magnetic interactions and calculate the mass, magnetic moment, binding energy, and relative strong decay width for the $nnQQ\bar{Q}$ system. We show that the binding energies of most states in the flavor combination $nncc\bar{c}$ are approximately $-20 \, \text{MeV}$, whereas states involving bottom quarks have binding energies around $-120 \, \text{MeV}$, with some decay widths suppressed by the decay constant. Additionally, the $nQQQ\bar{Q}$ system exhibits even deeper binding. Our results support the compact intention of $nnQQ\bar{Q}$ and suggest that the $nQQQ\bar{Q}$ configuration demonstrates even stronger compactness.

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arXiv2024

Masses and decays of triply-heavy pentaquarks

In this work, we study masses and decays of triply-heavy pentaquarks $QQQn\bar{n}(Q=b,c)$ in the unified MIT bag model. We construct the color-spin wave functions of the triply-heavy pentaquarks we address and use numerical variational method to compute all ground-state masses of these system. By excluding the scattering states in these configurations, we compute the decay width ratios of each decay channels relative to the maximum width for the compact pentaquark states, obtaining main decay modes of the triply-heavy pentaquark systems.

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arXiv2024

Triply heavy tetraquark states: masses and other properties

In this work, we study masses and other static properties of triply heavy tetraquarks in the unified framework of the MIT bag which incorporates chromomagnetic interactions and enhanced binding energy. The masses, magnetic moments and charge radii of all strange and nonstrange (ground) states of triply heavy tetraquarks are computed, suggesting that all of triply heavy tetraquarks are above the respective two-meson thresholds. We also estimate relative decay widths of main decay channels of two-heavy mesons for these tetraquarks.

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arXiv2023

Study of the hidden-heavy pentaquarks and $P_{cs}$ states

In light of the recently observed resonance states $P_{ψs}^Λ(4338)^0$ and $P_{cs}(4459)^0$ by LHCb Collaboration in $J/ψΛ$ decay channel, we perform a systematical study of all possible hidden-heavy pentaquarks with strangeness $S=0,-1,-2,-3$, in unified framework of MIT bag model. The color-spin wavefunctions presented in terms of Young-Yamanouchi bases and transformed into baryon-meson couplings, are utilized to calculate masses, magnetic moments and ratios of partial widths. With numerical analysis, the observed $P_{ψs}^Λ(4338)^0$ is likely to be a $1/2^-$ compact $P_{cs}$ pentaquark, and $P_{cs}(4459)^0$ favors two-peak structure of $3/2^-$ and $1/2^-$ $P_{cs}$ states. Further predictions on hadron properties and decay channels are given to compact $P_{css}$, $P_{csss}$ states and bottom sectors.

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arXiv2023

Mass spectra of hidden heavy-flavor tetraquarks with two and four heavy quarks

Inspired by the observation of the $X(6900)$ by LHCb and the $X(6600)$ (with mass $6552\pm 10$ $\pm 12$ MeV) recently by CMS and ATLAS experiments of the LHC in the di-$J/Ψ$ invariant mass spectrum, we systemically study masses of all ground-state configurations of the hidden heavy-flavor tetraquarks $q_{1}Q_{2}\bar{q}_{3}\bar{Q}_{4}$ and $Q_{1}Q_{2}\bar{Q}_{3}\bar{Q}_{4}$ ($Q=c,b$;$q=u,d,s$) contaning two and four heavy quarks in the MIT bag model with chromomagnetic interaction and enhanced binding energy. Considering color-spin mixing due to chromomagnetic interaction, our mass computation indicates that the observed $X(6600)$ is likely to be the $0^{++}$ ground states of hidden-charm tetraquark $cc\bar{c}\bar{c}$ with computed masses $6572$ MeV, which has a $0^{++}$ color partner around $6469$ MeV. The fully bottom system of tetraquark $bb\bar{b}\bar{b}$ has masses of 19685 MeV and 19717 MeV for the the $0^{++}$ ground states. Further computation is given to the tetraquark systems $sc\bar{s}\bar{c}$, $sb\bar{s}\bar{b}$, $cb\bar{c}\bar{b}$, $nc\bar{n}\bar{c}$ and $nb\bar{n}\bar{b}$, suggesting that the $Z_{c}(4200)$ is the tetraquark $nc\bar{n}\bar{c}$ with $J^{PC}=1^{+-}$. All of these tetraquarks are above their lowest thresholds of two mesons and unstable against the strong decays.

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arXiv2023

Doubly heavy tetraquarks: heavy quark bindings and chromomagnetically mixings

We introduce an enhanced binding energy $B_{QQ}$ between heavy-heavy quarks $QQ$ and a flux-tube correction into the chromomagnetic interaction model to study nonstrange doubly-heavy tetraquarks $T_{QQ}$ ($Q=c,b)$. A simple relation in terms of baryon masses is proposed to estimate the binding energies $B_{QQ}$ and thereby map the flux-tube corrections in doubly-heavy tetraquarks $T_{cc}$, $T_{bb}$ and $T_{bc}$. Our computation via diagonalization of chromomagnetic interaction predicts the doubly charmed tetraquark $T_{cc}$ (in color rep. $\bar{3}_{c}\otimes 3_{c}$) and $T_{cc}^{\ast }$ (in $6_{c}\otimes \bar{6}_{c}$) with $IJ^{P}=01^{+}$ to have masses of $3879.2$ MeV and $4287.6$ MeV, respectively, with the former being in consistent with the measured mass $3874.7\pm 0.05$ MeV of the doubly charmed tetraquark $T_{cc}(1^{+})=cc\bar{u}\bar{d}$ discovered by LHCb. Further mass predictions are given of the doubly bottom tetraquarks $T_{bb}$ and the bottom-charmed tetraquarks $T_{bc}$ with $J^{P}=0^{+},1^{+},2^{+}$ and $I=0,1$. A chromomagnetical mixing between the color configurations $\bar{3}_{c}\otimes 3_{c}$ and $6_{c}\otimes \bar{6}_{c}$ is noted for the bottom-charmed states $T_{bc}$ with $IJ^{P}=01^{+}$ and $IJ^{P}=1(0^{+},1^{+})$.

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arXiv2021

Masses and magnetic moments of hadrons with one and two open heavy quarks: heavy baryons and tetraquarks

In this work, we compute masses and magnetic moments of the heavy baryons and tetraquarks with one and two open heavy flavors in a unified framework of MIT bag model. Using the parameters of MIT bag model, we confirm that an extra binding energy, which is supposed to exist between heavy quarks ($c$ and $b$) and between heavy and strange quarks in literatures, is required to reconcile light hadrons with heavy hadrons. Numerical calculations are made for all light mesons, heavy hadrons with one and two open heavy flavors, predicting the masses of doubly charmed baryons to be $ M(Ξ_{cc})=3.604$ GeV, $ M(Ξ_{cc}^{\ast })=3.714$ GeV, and that of the strange isosinglet tetraquark $ud\bar{s}\bar{c}$ with $J^{P}=0^{+}$ to be $ M\left( ud\bar{s}\bar{c},0^{+}\right) =2.934$ GeV. The state mixing due to chromomagnetic interaction is shown to be sizable for the strange scalar tetraquark $nn\bar{s}\bar{c}$.

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arXiv2017

Quantum phase transitions of light in a dissipative Dicke-Bose-Hubbard model

The impacts that the environment has on the quantum phase transition of light in the DickeBose-Hubbard model are investigated. Based on the quasibosonic approach, mean field theory and the perturbation theory, the formulation of the Hamiltonian, the eigenenergies and the superfluid order parameter are obtained analytically. Compared with the ideal cases, the order parameter of the system evolves with time as the photons naturally decay in their environment. When the system starts with the superfluid state, the dissipation makes the photons tend to localize, and a greater hopping energy of photon is required to restore the long-range phase coherence of the localized state of the system. Furthermore, the Mott lobes disappears and the system tends to be classical with the number of atoms increasing; however, the atomic number is far lower than that expected under ideal circumstances. Therefore, our theoretical results offer valuable insight into the quantum phase transition of a dissipative system.

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