arXiv subjects

Xiao-Nan Li

Publications and source records attributed to Xiao-Nan Li.

14 recordsLinked to original sources

arXiv2026

Light-cone Distribution Amplitudes of Vector Mesons within the Self-Consistent Light-front Quark Model

In this paper, we investigate the twist-2 and twist-3 light-cone distribution amplitudes (LCDAs) of vector mesons within the self-consistent light-front quark model, and the $n$th Gegenbauer moment $a_n(μ)$, $ξ$-moment $\langle ξ^n\rangle^{\parallel(\perp)}$ and transverse moment $\langle \mathbf{k}^n_\perp\rangle^{\parallel(\perp)}$ are also carried out. Adopting the parameter set fixed by confinements from the mesonic decay constants, we perform the numerical analysis and the results reveal several key insights: (i) The flavor symmetry breaking effects are more pronounced in the twist-3 LCDAs of vector mesons, which leads to the establishment of $a_1^\perp>a_1^\parallel$ and $\langle ξ^n\rangle^\perp>\langle ξ^n\rangle^\parallel$. This is consistent with previous findings in research for the LCDAs of pseudoscalar mesons. (ii) For vector mesons, the twist dependence decreases in the heavy quark limit which lead to $ϕ_{2}^\parallel(x)\simeqϕ_{3}^\perp(x)$. For pseudoscalar and vector mesons composed of the same quark constituents, their LCDAs with the same twist exhibit similarity and gradually converge as the increasing of quark mass, i.e., $ϕ_{2}^A(x)\simeqϕ_{2}^\parallel(x)$ and $ϕ_{3}^P(x)\simeqϕ_{3}^\perp(x)$ in $m_q\rightarrow\infty$. In the heavy-quark limit within the self-consistent LFQM framework, we find an approximate correlated spin-twist independence pattern, with $ϕ_2^A(x) \simeq ϕ_2^{\parallel}(x) \approxϕ_3^P(x) \simeq ϕ_3^{\perp}(x)$, resulting from the suppression of twist dependence and the approximate spin independence between pseudoscalar and vector mesons.

hep-ph↗

arXiv2026

Quarkonium light-cone distribution amplitudes: twist structure and mass dependence

We present a systematic study of the leading- and next-to-leading-twist light-cone distribution amplitudes (LCDAs) of ground-state pseudoscalar and vector quarkonium within the light-front quark model (LFQM). By implementing the replacement $M \to M_0$, we analyze the longitudinal and transverse structures of the LCDAs, together with their Gegenbauer moments, $ξ$-moments, and transverse momentum moments. We show that charge-conjugation symmetry enforces the exact vanishing of all odd Gegenbauer moments and odd $ξ$-moments. For pseudoscalar quarkonium, the twist-2 and twist-3 LCDAs become identical, which leads to the same Gegenbauer moments, $ξ$-moments, and transverse momentum moments. For vector quarkonium, although the twist-2 and twist-3 LCDAs differ in the case of finite quark masses, they progressively converge as the quark mass increases. In the heavy-quark limit, all quarkonium LCDAs satisfy $ϕ^A_{2} = ϕ^P_{3} \simeq ϕ^{\parallel}_{2} \simeq ϕ^{\perp}_{3}$, demonstrating an emergent twist-independence of quarkonium distribution amplitudes. We further find that the LCDAs become increasingly peaked and narrower with increasing quark mass, indicating that the meson system becomes increasingly close to a nonrelativistic bound state, with a more uniform and stable distribution of internal longitudinal momentum. For all quarkonium, the peak value exhibits a simple phenomenological scaling behavior governed by the ratio $m/β$. The transverse momentum moments increase with the meson mass, indicating a progressively more compact bound-state structure. These results reveal a universal and systematic evolution of quarkonium LCDAs driven by the quark mass.

hep-ph↗

arXiv2026

Distribution Amplitudes of Pseudoscalar Mesons within the Light-Front Quark Model

In this paper, we investigate the distribution amplitudes (DAs) of pseudoscalar mesons within the light-front quark model (LFQM), and the $n$-th Gegenbauer moment $a_n(μ)$, $ξ$-moment $\langle ξ^n\rangle$ and transverse moment $\langle \mathbf{k}^n_\perp\rangle$ are also studied. Two parameter sets are adopted by fitting to mesonic decay constants or mass spectra, leading to distinct schemes for numerical analysis. Our results reveal several key insights: (1) Under scheme-I, the second Gegenbauer moment for the pion, $a_{2,π} = 0.054$, is in excellent agreement with predictions from the platykurtic model and the nonlocal chiral quark model (NL$χ$QM). Meanwhile, scheme-II yields $a_{2,π} = 0.126$, which is consistent with lattice QCD (LQCD), Dyson-Schwinger equation (DSE) and data-driven light-cone sum rules (LCSR) analyses. Furthermore, we observe that $ϕ_{2,π} = ϕ^P_{3,π}$ with the replacement $M \to M_0$. (2) Flavor symmetry breaking effects are found to be more significant in higher-twist DAs, with a notable relation $a_1^P\approx 2 a_1$ emerging in heavy meson systems. (3) Interestingly, numerical analysis indicates that the transverse moment $\langle \mathbf{k}^n_\perp\rangle$ is twist-independent with the replacement $M\to M_0$. Additionally, we propose an empirical scaling relation $\frac{Δm^{0.61}}{β^{1.10}}x_p=0.67$ to effectively describe the shape of DAs for heavy mesons. Collectively, these results demonstrate that mass asymmetry remarkably influences DAs and kinds of moments, these theoretical predictions will be tested in future experiments.

hep-ph↗

arXiv2025

The Electromagnetic Form Factors of Pseudoscalar Mesons within the Light-Front Quark Model

In this paper, we investigate the electromagnetic form factors (EMFFs) and charge radii of pseudoscalar mesons within the light-front quark model (LFQM). Using parameters derived from the confinement of mesonic decay constants, we obtain numerical results, which indicate the following: (i) The EMFFs of charged and neutral mesons exhibit significant differences in their endpoint behaviors but show similar asymptotic behavior in the high momentum transfer ($Q^2$) regions. For the EMFFs of light mesons such as $π$ and $K^+$, our results are in excellent agreement with experimental data in the low $Q^2$ regions. For the charge radii of mesons, our results also show rough consistency with predictions from other approaches. (ii) For charged mesons, the peak values of $Q^2 F_P(Q^2)$ are approximately proportional to the mass difference $Δm$ between their constituent quarks. Moreover, the mean square radii $\left\langle r^2 \right\rangle_P$ of charged mesons decrease with increasing meson mass and decreasing $Δm$. For neutral mesons, their charge radii are primarily determined by the electric charge of the heavy quark. These results indicate that quark mass asymmetry significantly influences the behavior of the EMFFs and charge radii of mesons. Experimental data to test these predictions would thus be of great interest.

hep-ph↗

arXiv2025

The $ρ$-meson electromagnetic form factors within the light-front quark model

In this paper, we study the $ρ$-meson electromagnetic form factors (EMFFs) within the framework of light-front quark model (LFQM). The physical form factors $G_{C,M,Q}(Q^2)$ of $ρ$-meson as well as the charged square radius $\langle r^2\rangle$, the magnetic moment $μ$ and the quadrupole moment $\bar Q$ are calculated, which describe the behaviors of EMFFs at zero momentum transfer. Using the type-II replacement, we find that the zero-mode does contribute zero to the matrix element $S_{00}^+$. It is found that the ``$M\to M_{0}$" replacement improves angular condition remarkably, which permits different prescriptions of $ρ$-meson EMFFs give the consistent results. The residue tiny violation of angular condition needs other explanations than the zero-mode contributions. Our results indicate that the relativistic effects or interaction internal structure are weaken in the zero-binding limit. This work is also applied for the other spin-1 particles.

hep-ph↗

arXiv2020

Probing new physics in semileptonic $Σ_b$ and $Ω_b$ decays

Recently, several hints of lepton non-universality have been observed in the semileptonic B meson decays in terms of both in the neutral current ($b\to s l \bar{l}$) and charged current ($b\to c l \bar{ν_{l}}$) transitions. Motivated by these inspiring results, we perform the analysis of the baryon decays ${Σ_b}\to Σ_c l \bar{ν_{l}}$ and $Ω_b\to Ω_c l \bar{ν_{l}} (l=e,μ,τ)$ which are mediated by $ b \to c l \bar{ν_{l}}$ transitions at the quark level, to scrutinize the nature of new physics (NP) in the model independent method. We first use the experimental measurements of $\mathcal{B}( B\to D^{(*)} l\bar{ν_{l}})$, ${\rm R}_{D^{(*)}}$ and ${\rm R}_{J/ψ}$ to constrain the NP coupling parameters in a variety of scenarios. Using the constrained NP coupling parameters, we report numerical results on various observables related to the processes ${Σ_b}\to Σ_c l \bar{ν_{l}}$ and $Ω_b\to Ω_c l \bar{ν_{l}}$, such as the branching ratios, the ratio of branching fractions, the lepton side forward-backward asymmetries, the hadron and lepton longitudinal polarization asymmetries and the convexity parameter. We also provide the $q^2$ dependency of these observables and we hope that the corresponding numerical results in this work will be testified by future experiments.

hep-ph↗

arXiv2020

Study of $b\to c$ induced $\bar{B}^* \to V \ell \barν_\ell$ decays

In this paper, we investigate the tree-dominated $\bar{B}^*_{u,d,s,c} \to V \ell^- \barν_\ell$ ($V=D^*_{u,d}\,,D^*_s\,,J/ψ$ and $\ell=e\,,μ\,,τ$) decays in the Standard Model with the relevant form factors obtained in the light-front quark model. These decays involve much more helicity states relative to the corresponding $\bar{B}^* \to P \ell^- \barν_\ell$ and $\bar{B} \to V \ell^- \barν_\ell$ decays, and moreover, the contribution of longitudinal polarization mode ($V$ meson) is relatively small, $\sim 30\%$, compared with the corresponding $B$ meson decays. We have also computed the branching fraction, lepton spin asymmetry, forward-backward asymmetry and ratio $R_V^{\ast(L)}\equiv \frac{\mathcal{B}(\bar{B}^*\to Vτ^- \barν_τ)}{\mathcal{B}(\bar{B}^*\to V \ell^{\prime-} \barν_{\ell^{\prime}})}$ ($\ell'=e\,,μ$). Numerically, the branching fractions of $\bar{B}^* \to V \ell^{\prime-} \barν_{\ell^{\prime}}$ decays are at the level of ${\cal O}(10^{-7})$, and are hopeful to be observed by LHC and Belle-II experiments. The ratios $R_{D^*\,,D^*_s\,,J/ψ}^{\ast(L)}$ have relatively small theoretical uncertainties and are close to each other, $R^{*(L)}_{D^*}\simeq R^{*(L)}_{D^*_s}\simeq R^{*(L)}_{J/ψ} \simeq [0.26,0.27]~([0.27,0.29])$, which are a bit different from the predictions in some previous works. The future measurements are expected to make tests on these predictions.

hep-ph↗

arXiv2019

Form factors of $V'\to V''$ transition within the light-front quark models

In this paper, we calculate the matrix element and form factors of vector-to-vector ($V'\to V'$) transition within the standard light-front~(SLF) and covariant light-front~(CLF) quark models~(QMs), and investigate the self-consistency and Lorentz covariance of the CLF QM within two types of correspondences between the manifest covariant Bethe-Salpeter approach and the LF approach. The zero-mode and valence contributions to the form factors of $V'\to V'$ transition in the CLF QM and their relation to the SLF results are analyzed, and the main conclusions obtained via the decay constants of vector and axial-vector mesons and form factors of $P\to V$ transition in the previous works are confirmed again. Furthermore, we present our numerical predictions for the form factors of $c\to (q,s)$ ($q=u,d$) induced $D^*\to (K^*\,,ρ)$, $D^*_s\to (ϕ\,,K^*)$, $J/Ψ\to (D^*_s\,,D^*)$, $B^*_c\to (B^*_s\,,B^*)$ transitions and $b\to (q,s,c)$ induced $B^*\to (D^*\,,K^*\,,ρ)$, $B^*_s\to (D^*_s\,,ϕ\,,K^*)$, $B^*_c\to (J/Ψ\,,D^*_s\,,D^*)$, $Υ(1S)\to (B_c^*\,,B_s^*\,,B^*)$ transitions, which can be applied further to the relevant phenomenological studies of meson decays.

hep-ph↗

arXiv2019

Revisiting the form factors of $P\to V$ transition within the light-front quark models

We investigate the self-consistency and Lorentz covariance of the covariant light-front quark model~(CLF QM) via the matrix elements and form factors~(${\cal F}=g$, $a_{\pm}$ and $f$) of $P\to V$ transition. Two types of correspondence schemes between the manifest covariant Bethe-Salpeter approach and the light-front quark model are studied. We find that, for $a_{-}(q^2)$ and $f(q^2)$, the CLF results obtained via $\lbd=0$ and $\pm$ polarization states of vector meson within the traditional type-I correspondence scheme are inconsistent with each other; and moreover, the strict covariance of the matrix element is violated due to the nonvanishing spurious contributions associated with noncovariance. We further show that such two problems have the same origin and can be resolved simultaneously by employing the type-II correspondence scheme, which advocates an additional replacement $M\to M_0$ relative to the traditional type-I scheme; meanwhile, the results of ${\cal F}(q^2)$ in the standard light-front quark model~(SLF QM) are exactly the same as the valence contributions and equal to numerally the full results in the CLF QM, {\it i.e.}, $[{\cal{F}}]_{\rm SLF}=[{\cal{F}}]_{\rm val.}\doteq[{\cal{F}}]_{\rm full}$. The numerical results for some $P\to V$ transitions are updated within the type-II scheme. Above findings confirm the conclusion obtained via the decay constants of vector and axial-vector mesons in the previous works.

hep-ph↗

arXiv2018

Self-consistency and covariance of light-front quark models: testing via $P$, $V$ and $A$ meson decay constants, and $P\to P$ weak transition form factors

In this paper, we test the self-consistencies of the standard and the covariant light-front quark model and study the zero-mode issue via the decay constants of pseudoscalar ($P$), vector ($V$) and axial-vector ($A$) mesons, as well as the $P\to P$ weak transition form factors. With the traditional type-I correspondence between the manifestly covariant and the light-front approach, the resulting $f_{V}$ as well as $f_{^1\!A}$ and $f_{^3\!A}$ obtained with the $\lbd=0$ and $\lbd=\pm$ polarization states are different from each other, which presents a challenge to the self-consistency of the covariant light-front quark model. However, such a self-consistency problem can be "resolved" within the type-II scheme, which requires an additional replacement $M\to M_0$ relative to the type-I case. Moreover, the replacement $M\to M_0$ is also essential for the self-consistency of the standard light-front quark model. In the type-II scheme, the valence contributions to the physical quantities~(${\cal Q}$) considered in this paper are alway the same as that obtained in the standard light-front quark model, $[{\cal Q}]_{\rm val.}=[{\cal Q}]_{\rm SLF}$, and the zero-mode contributions to $f_{V,^1\!A,^3\!A}$ and $f_-(q^2)$ exist only formally but vanish numerically, which implies further that $[{\cal Q}]_{\rm val.}\dot{=} [{\cal Q}]_{\rm full}$. In addition, the manifest covariance of the covariant light-front quark model is violated in the traditional type-I scheme, but can be recovered by taking the type-II scheme.

hep-ph↗

arXiv2018

Decay constants of pseudoscalar and vector mesons with improved holographic wavefunction

We calculate the decay constants of light and heavy-light pseudoscalar and vector mesons with improved soft-wall holographic wavefuntions, which take into account the effects of both quark masses and dynamical spins. We find that the predicted decay constants, especially for the ratio $f_V/f_P$, based on light-front holographic QCD, can be significantly improved, once the dynamical spin effects are taken into account by introducing the helicity-dependent wavefunctions. We also perform detailed $χ^2$ analyses for the holographic parameters ({\it i.e.} the mass-scale parameter $κ$ and the quark masses), by confronting our predictions with the data for the charged-meson decay constants and the meson spectra. The fitted values for these parameters are generally in agreement with those obtained by fitting to the Regge trajectories. At the same time, most of our results for the decay constants and their ratios agree with the data as well as the predictions based on lattice QCD and QCD sum rule approaches, with only a few exceptions observed.

hep-ph↗

arXiv2017

Study of the weak annihilation contributions in charmless $B_s\to VV$ decays

In this paper, in order to probe the spectator-scattering and weak annihilation contributions in charmless $B_s\to VV$ (where $V$ stands for a light vector meson) decays, we perform the $χ^2$-analyses for the end-point parameters within the QCD factorization framework, under the constraints from the measured $\bar B_{s}\to$$ρ^0ϕ$, $ϕK^{*0}$, $ϕϕ$ and $K^{*0}\bar K^{*0}$ decays. The fitted results indicate that the end-point parameters in the factorizable and nonfactorizable annihilation topologies are non-universal, which is also favored by the charmless $B\to PP$ and $PV$ (where $P$ stands for a light pseudo-scalar meson) decays observed in the previous work. Moreover, the abnormal polarization fractions $f_{L,\bot}(\bar B_{s}\to K^{*0}\bar K^{*0})=(20.1\pm7.0)\%\,,(58.4\pm8.5)\%$ measured by the LHCb collaboration can be reconciled through the weak annihilation corrections. However, the branching ratio of $\bar B_{s}\toϕK^{*0}$ decay exhibits a tension between the data and theoretical result, which dominates the contributions to $χ_{\rm min}^2$ in the fits. Using the fitted end-point parameters, we update the theoretical results for the charmless $B_s\to VV$ decays, which will be further tested by the LHCb and Belle-II experiments in the near future.

hep-ph↗

arXiv2016

Fits of Weak Annihilation and Hard Spectator Scattering Corrections in $B_{u,d}\to VV$ Decays

In this paper, the contributions of weak annihilation and hard spectator scattering in $B\to ρK^*$, $ K^* \bar{K}^*$, $ϕK^*$, $ρρ$ and $ϕϕ$ decays are investigated within the framework of QCD factorization. Using the experimental data available, we perform $χ^2$ analyses of end-point parameters in four cases based on the topology-dependent and polarization-dependent parameterization schemes. The fitted results indicate that: (i) In the topology-dependent scheme, the relation $(ρ_A^{i},ϕ_A^{i})\neq (ρ_A^{f},ϕ_A^{f})$ gotten through $B\to PP$ and $PV$ decays is favored by the penguin-dominated $B\to VV$ decays at 95\% C. L., (ii) The large hard spectator scattering corrections and/or the simplification $ (ρ_H,ϕ_H)= (ρ_A^{i},ϕ_A^{i})$ are challenged by ${\cal B}(\bar{B}^0\to ρ^0 ρ^0)$, even though they are allowed by $B\to PP$ and $PV$ decays and helpful for resolving "$ππ$ puzzle", (iii) In the polarization-dependent scheme, the relation $(ρ_A^{L},ϕ_A^{L})\neq (ρ_A^{T},ϕ_A^{T})$ is always required. Moreover, we have updated the theoretical results for $B\to VV$ decays with the best-fit values of end-point parameters. A few observables, such as the ones of pure annihilation $B_d\to ϕϕ$ decay, are also identified for probing the annihilation corrections.

hep-ph↗

arXiv2016

Evaluation of new large area PMT with high quantum efficiency

The neutrino detector of the Jiangmen Underground Neutrino Observatory (JUNO) is designed to use 20 kilotons of liquid scintillator and approximately 16,000 20-inch photomultipliers (PMTs).One of the options is to use the 20-inch R12860 PMT with high quantum efficiency which has recently been developed by Hamamatsu Photonics. The performance of the newly developed PMT preproduction samples is evaluated. The results show that its quantum efficiency is $30\%$ at $400 nm$. Its Peak/Valley (P/V) ratio for the single photoelectron is 4.75 and the dark count rate is $27 kHz$ at the threshold of 3 mV while the gain is at $1 \times 10^7$. The transit time spread of a single photoelectron is $2.86 ns$. Generally the performances of this new 20-inch PMT are improved over the old one of R3600.

physics.ins-det↗