arXiv subjects

Sheng-Qi Zhang

Publications and source records attributed to Sheng-Qi Zhang.

14 recordsLinked to original sources

arXiv2026

Discriminating baryonium and final-state-interaction interpretations of $X(2356)$

We revisit the $X(2356)$ enhancement observed by BESIII in $e^+e^-\toΛ\barΛη$ from the viewpoint of near-threshold dynamics. Motivated by the possibility of light $Λ\barΛ$ baryonium, we compare this interpretation with final-state-interaction (FSI) explanations within a minimal FSI-dressed pole framework. Fits of the pure-FSI, baryonium-like-pole, and mixed pole--continuum scenarios to the digitized BESIII spectrum identify the energy-dependent FSI description as providing the best balance between fit quality and model complexity. The extracted pole positions depend strongly on the amplitude parametrization, demonstrating the sensitivity of the baryonium interpretation to the treatment of the continuum. We discuss how decay channels, spin observables, and partner searches can provide complementary constraints on the dynamics underlying the enhancement.

hep-ph↗

arXiv2026

Decipher the nature of glueball candidate $X(2370)$

As a unique form of matter composed entirely of gauge bosons, glueballs are an important low-energy prediction of QCD. After decades of searches, the BESIII Collaboration recently suggested that $X(2370)$ may contain a dominant glueball component, based largely on evidence that it is approximately a flavor singlet. Recognizing that flavor-singlet character does not uniquely identify a glueball, we perform a comprehensive analysis using available mass, flavor-singlet, and decay constraints. We find that three flavor-singlet configurations-hybrid meson, tetraquark state, and trigluon glueball-can satisfactorily reproduce the existing experimental data. Among these possibilities, the hybrid structure best describes the measured three-pseudoscalar decay ratios. To ultimately pin down the dominant structure of $X(2370)$, we propose measuring the decay-width ratios $a_0(1450)π/[K_0^*(1430)\bar K+\mathrm{c.c.}]$ and $ϕϕ/[b_1(1235)ρ]$, which can exclusively distinguish these three scenarios.

hep-ph↗

arXiv2026

Strange pentaquark molecules in QCD sum rules

We study hidden- and open-strange pentaquark configurations in the hadronic molecular picture with QCD sum rules. Starting from the baryon octet combined with an $s\bar{s}$ pair, we construct 21 interpolating currents with $J=1/2$ and $3/2$. In the analysis, contributions up to dimension 11 are included in the operator product expansion, and both parity-projected spectra and the chiral-even and chiral-odd Lorentz structures are examined. No bound-state solution is found in the $J^P=1/2^-$ sector, although several channels generate resonance masses near nearby thresholds or poorly established strange baryons. In the $J^P=3/2^-$ sector, the $Σϕ$ and $ΞK^\ast$ currents both support a near-threshold bound-state solution around $2.2$ GeV, suggesting a possible molecular configuration with channel mixing. In contrast, positive-parity sectors are more difficult to identify the corresponding states. In addition, our results favor the spin-parity assignments $J^P=3/2^-$ for $Σ(2250)$, $J^P=1/2^-$ for $Σ(2455)$, $Σ(2620)$, and $Ξ(2370)$, and $J^P=3/2^+$ for $Ξ(2250)$. These results provide a systematic QCD sum rule study of strange pentaquark molecular candidates in the strange sector.

hep-ph↗

arXiv2026

Baryons and baryoniums in the perspective of QCD sum rules

Following the experimental confirmation of tetraquark and pentaquark states, the search for hexaquark states has emerged as a new frontier in hadron physics. The recent observation of $X(1840)$ and $X(1880)$ by BESIII collaboration has provided evidence for the predicted $p\bar{p}$ bound states. Such baryon-antibaryon configurations, encompassing both bound states and resonances, are commonly referred to as baryoniums and are regarded as promising hexaquark candidates. In this article, we provide a comprehensive review of the investigations into baryonium states and their constituents, i.e., baryons, within the framework of QCD sum rules. We delineate the fundamental calculation procedures of this method to facilitate its practical application and benchmark the theoretical predictions against alternative models as well as the latest experimental data.

hep-ph↗

arXiv2026

Nodal mechanism for the suppressed $D\bar D$ decay of $ψ(4040)$ in the Bethe--Salpeter framework

The strong decay $ψ(4040)\to D\bar D$ is anomalously suppressed despite ample phase space, whereas the $D\bar D^*$ and $D_s\bar D_s$ channels remain sizable. In this work, we study this suppression and the associated open-charm hierarchy in the framework of the instantaneous Bethe--Salpeter equation combined with the relativistic $^3P_0$ model, with the pair-creation strength fixed independently from $ψ(3770)\to D\bar D$. Within this framework, we show that the suppressed $D\bar D$ mode can be understood as a consequence of node-induced cancellations in the relativistic decay amplitude. The $D\bar D$ amplitude is strongly reduced because the corresponding overlap integral receives comparable positive and negative contributions from different momentum regions, whereas the $D\bar D^*$ and $D_s\bar D_s$ channels do not undergo the same strong cancellation. This interpretation is further supported by the pronounced sensitivity of the $D\bar D$ width to the initial mass, the charged-neutral $D$-meson mass splitting, and the dip structure in the mass dependence of the partial width. Our results provide a dynamical explanation of the suppressed $D\bar D$ mode and the core open-charm hierarchy of $ψ(4040)$ within a conventional $3\,{}^3S_1$ charmonium picture, while the precise value of the near-vanishing $D\bar D$ width remains model dependent.

hep-ph↗

arXiv2026

Spectrum of Light Hexaquark States in Triquark-antitriquark Configuration

To understand the nature of $X(2075)$ and $X(2085)$ observed by the BESIII collaboration in the $p\barΛ$ system, we systematically investigate the possibility that these states are compact hexaquark with triquark-antitriquark configurations for the first time. Within the framework of QCD sum rules, the mass spectrum and decay constants of such hexaquark states with quantum numbers $J^P=0^-, 0^+, 1^-, 1^+$ are studied. Consequently, six independent and nondegenerate hexaquark candidates are obtained, among which two $J^P = 1^-$ states exhibit masses consistent with $X(2075)$, while the two $J^P = 1^+$ states differ markedly from the mass of $X(2075)$ or $X(2085)$. The remaining two states with $J^P = 0^+$ and $0^-$ may serve as predictions for potential compact hexaquark configurations. Furthermore, the possible decay modes of these hexaquark states are analyzed, which could be the experimental signatures for their identification.

hep-ph↗

arXiv2026

Mastering Olympiad-Level Physics with Artificial Intelligence

Olympiad-level physics problem-solving significantly challenges both humans and artificial intelligence (AI), as it requires integrating appropriate modeling, application of physical principles, and precise calculation within long reasoning processes. In this paper, we introduce LOCA (LOgical Chain Augmentation), an AI agent framework designed for complex physics reasoning. LOCA decomposes long reasoning into serialized atomic and verifiable steps, refining the solution through an augment-review loop. We evaluate LOCA on the 2025 Chinese Physics Olympiad (CPhO) theory examination, a rigorous testbed renowned for its depth and complexity. The framework achieves a near-perfect score of 313 out of 320 points, significantly surpassing the top human competitor and other baseline methods. Furthermore, LOCA attains a near-perfect score of 28.6 out of 30 on the IPhO 2025 examination, demonstrating its strong generalizability across different contexts. Our work points toward the development of trustworthy AI partners in both research and education.

cs.CL↗

arXiv2026

The Spectra of $p\barΛ$ and $p\barΣ$ Hexaquark States

Motivated by the observation of the $J^P = 1^+$ resonance $X(2085)$ in the $p\barΛ$ system by the BESIII collaboration, we studied the molecular states of hexaquarks $p\barΛ$ and $p\barΣ$ with baryon-antibaryon structures within the framework of the QCD sum rules. Non-perturbative contributions up to dimension 13 were considered in our analysis. The results indicate the existence of six possible molecular states $p\barΛ$ and $p\barΣ$, with quantum numbers $J^{P}=0^{-}, 0^{+}, 1^{-}$. Consequently, the current sum rule results do not support the interpretation of $X(2085)$ as a $p\barΛ$ or $p\barΣ$ molecular state. On the other hand, we find that the masses of the proposed $p\barΛ$ and $p\barΣ$ structures with $J^{P} = 1^{-}$ are in the vicinity of observed $X(2075)$, which implies that the nature of this state needs more invistigations. Moreover, the possible decay modes of the concerned hexaquark states are analyzed.

hep-ph↗

arXiv2024

Rare $ Λ_c $ decays and new physics effects

Recent experimental progress on baryonic rare decays has spurred a deeper investigation on flavor-changing neutral current transitions in the baryon sector. Within the framework of QCD sum rules, we derive a complete set of form factors for the $ Λ_c\to p $ process in the large recoil region and use the $z$-series parametrization to extrapolate them across the full physical range. Employing these form factors and flavor symmetries, we compute branching fractions for the decays $Λ_c \to p e^+ e^-$ and $Λ_c \to p μ^+ μ^-$, as well as for rare $ Ξ_c $ decay modes. We examine as well the new physics effects through specific angular observables such as the lepton forward-backward asymmetry and the fraction of longitudinally polarized dileptons. Results indicate that new physics models may be testified in baryonic rare decays, with immense data collected in running and future colliders.

hep-ph↗

arXiv2024

Hyperon semileptonic decays in QCD sum rules

We investigate the hyperon semileptonic decays within the framework of QCD sum rules. The flavor $ SU(3) $ symmetry breaking effects are analyzed via the relevant form factors and corresponding branching fractions. Employing the $ z $-series parameterization to capture the $ q^2 $ dependence of form factors, we calculate the hyperon semileptonic decay rates and confront them with the recent experimental measurements. Moreover, we calculate as well the non-standard tensor form factors, which involve certain new physics beyond the standard model.

hep-ph↗

arXiv2023

$ Λ_c $ semileptonic decays

Motivated by the recent experimental progress in the $ Λ_c $ decay that contains a neutron in the final state, we analyze the semileptonic decay $ Λ_c \rightarrow n \ell ν_\ell $ in the framework of QCD sum rules. The transition form factors are analytically computed using three-point correlation functions and the Cutkosky cutting rules, which can be extrapolated into the physical region by employing the $ z $-series parametrization. The branching fractions of $ Λ_c \rightarrow n e^+ ν_e $ and $ Λ_c \rightarrow n μ^+ ν_μ $ are estimated to be $ (0.281\pm 0.056)\%$ and $ (0.275\pm 0.055)\% $, respectively. Furthermore, we calculate as well the relevant decay asymmetry observables sensitive to new physics beyond the standard model. The numerical results of semileptonic decays $ Λ_c \rightarrow Λ\ell ν_\ell $ are also given and confronted to the latest experimental data.

hep-ph↗

arXiv2022

Gluonic nature of the newly observed state $X(2600)$

Motivated by the newly observed resonance $X(2600)$ by BESIII Collaboration, we examine the trigluon glueball interpretation for it in the framework of QCD sum rules. We evaluate the mass spectra of the trigluon glueballs with quantum numbers $0^{-+}$ and $2^{-+}$ up to dimension 8 condensate in the operator product expansion. Our numerical results indicate that the mass of the $2^{-+}$ trigluon glueball is about $2.66\pm 0.06$ GeV, which is consistent with the mass of the X(2600) within the uncertainties, while $0^{-+}$ has a mass of $2.01\pm0.14$ GeV. The possible decay channels of the $2^{-+}$ state are analyzed, which are crucial in decoding $X(2600)$'s internal structure and are hopefully measurable in BESIII, BEllEII, PANDA, and LHCb experiments.

hep-ph↗

arXiv2022

Possible structure of the newly found exotic state $η_1(1855)$

Recently, a hadronic state named $η_1(1855)$, about 1.86 GeV, was observed in the BESIII experiment. This finding has a peculiar interest due to its exotic quantum number $J^{PC}=1^{-+}$. In this paper, we examine the tetraquark interpretation for the structure of $η_1(1855)$ in the configurations of $[1_c]_{\bar{s}s}\otimes[1_c]_{\bar{q}q}$ and $[1_c]_{\bar{s}q}\otimes[1_c]_{\bar{s}q}$, and perform a mass spectrum calculation in the framework of QCD sum rules. The results show that the observed $η_1(1855)$ could be embedded into the $[1_c]_{\bar{s}s}\otimes[1_c]_{\bar{q}q}$ configuration. The possible tetraquark and hybrid decay modes are analyzed, which are critical in decoding its inner structure. In the same way, we evaluate as well the $\bar{s}s\bar{s}s$ molecular state with $1^{-+}$ quantum number and find that there might exist two such ground states.

hep-ph↗

arXiv2022

Light baryonium spectrum

We evaluate the light baryonium spectrum, viz. the baryon-antibaryon states, in the framework of QCD sum rules. The nonperturbative contributions up to dimension 12 are taken into account. Numerical results indicate that there might exist eight possible light baryonium states, i.e. $p$-$\bar{p}$, $Λ$-$\barΛ$, $Σ$-$\barΣ$, and $Ξ$-$\barΞ$ with quantum numbers of $0^{-+}$ and $1^{--}$. For the $Λ$-$\barΛ$, $Σ$-$\barΣ$, and $Ξ$-$\barΞ$ states, their masses are found above the corresponding dibaryon thresholds, while the masses of $p$-$\bar{p}$ states are not. The possible baryonium decay modes are analyzed, which are hopefully measurable in BESIII, BELLEII, and LHCb experiments.

hep-ph↗