arXiv subjects

Xian-Wei Kang

Publications and source records attributed to Xian-Wei Kang.

At least 19 recordsLinked to original sources

arXiv2026

Magnetic moments of open bottom--charm molecular pentaquark octets

We present a comprehensive theoretical investigation of the magnetic moments of open heavy-flavor molecular pentaquarks with quark compositions $b\bar{c}qqq$ and $c\bar{b}qqq$ (where $q=u,d,s$). Employing a molecular picture in which the pentaquarks are treated as S-wave bound states of a heavy baryon and a meson, we systematically construct the complete spin--flavor wavefunctions for the two distinct SU(3)$_f$ octet representations, $8_{1f}$ and $8_{2f}$, arising from symmetric and antisymmetric light-diquark configurations, respectively. Within the framework of the constituent quark model, we calculate the magnetic moments of spin-parity configurations, $J^P = \frac{1}{2}^-(\frac{1}{2}^+\otimes 0^-)$ and $J^P = \frac{1}{2}^-, \frac{3}{2}^-(\frac{1}{2}^+\otimes 1^-)$, for each member of the $b\bar{c}$ and $c\bar{b}$ octets. Our results reveal a striking hierarchy: in the $8_{2f}$ representation, the $\frac{1}{2}^+\otimes 0^-$ states exhibit near-universal magnetic moments ($μ\approx -0.062\,μ_N$ for $b\bar{c}qqq$ and $μ\approx +0.362\,μ_N$ for $c\bar{b}qqq$), as a direct consequence of the spin-singlet light-diquark that suppresses light-quark contributions. In contrast, the $8_{1f}$ representation shows a broad spectrum of values with frequent sign changes, reflecting the active role of the symmetric light-diquark. The clear differences between the $b\bar{c}$ and $c\bar{b}$ families demonstrate explicit heavy-quark flavor symmetry breaking in electromagnetic observables. These predictions provide a detailed set of electromagnetic benchmarks that can serve as discriminants for the internal flavor structure and spin configuration of future experimentally observed open heavy-flavor pentaquarks, offering valuable guidance for ongoing and future searches at facilities such as LHCb and Belle II.

hep-ph↗

arXiv2026

Exploring new physics in the angular distribution of $\bar B\rightarrow D^*(\rightarrow Dπ)τ^-(\rightarrow V^-ν_τ)\barν_τ$

The decays $\bar{B}\rightarrow D^*τ^{-}\barν_τ$ provide sensitive probes of new physics in the $b\rightarrow cτν$ transition. We discuss the effects of new physics in the decay chain $\bar{B}\rightarrow D^*(\rightarrow Dπ)τ^{-}(\rightarrow V^-ν_τ)\barν_τ$ where $V$ is a vector meson. We first present a comprehensive analysis of the five-dimensional angular distribution for the full decay chain $\bar{B}\rightarrow D^*(\rightarrow Dπ)τ^{-}(\rightarrow ρ^-ν_τ)\barν_τ$, exploiting the hadronic $τ$ decay to $ρ^-ν_τ$ to circumvent the experimental challenge of direct $τ$ reconstruction. The differential decay rate is expressed in terms of measurable kinematic variables $θ^*$, $E_ρ$, $θ_ρ$, $χ_ρ$, and $q^2$ -- with complete coefficient functions provided for scalar, pseudoscalar, vector, axialvector, and tensor new-physics interactions. From this distribution we construct a set of integrated observables, including the $D^*$ polarization fractions and lepton-side forward-backward and azimuthal asymmetries, which isolate distinct combinations of helicity amplitudes. We further perform a numerical analysis using current experimental data on $R_{D^*}$ and the $D^*$ longitudinal polarization fraction $\langle F_L^{D^*}\rangle$ to constrain the complex new-physics couplings $g_L$, $g_R$, $g_P$, and $g_T$, revealing the correlations among them. Our formalism is also applicable to $τ\to a_1 ν_τ$, where the $3π$ final states mainly come from the $a_1$ meson. The framework established here provides a powerful tool for disentangling new-physics scenarios with future high-statistics data.

hep-ph↗

arXiv2026

Exclusive semileptonic $B$ decays to the ground and excited states of light mesons

Exclusive semileptonic decays of $B$ mesons to the ground, radially and orbitally excited states of light mesons are investigated in the framework of the relativistic quark model based on the quasipotential approach. Such decays are very important for the determination of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{ub}|$ and testing the nature of the excited light mesons. The mixing schemes for the isoscalar light mesons are considered. The possible assignment of the experimentally observed excited light mesons to the particular states is discussed. The form factors parameterizing weak decay matrix elements between the initial $B$ meson and final light mesons are calculated with the complete account of the relativistic effects, including contributions of the intermediate negative energy states and relativistic transformations of the meson wave functions from rest to the moving reference frame. As a result the transferred momentum squared, $q^2$, dependence of the form factors is explicitly determined in the whole accessible kinematical range. On the basis of the helicity formalism the decay branching fractions and asymmetry and polarization parameters are calculated. The obtained results for the semileptonic $B$ decays to the ground states of light mesons are confronted with available experimental data. On this basis the value of the $|V_{ub}|$ matrix element is determined. It is found in good agreement with the value extracted from inclusive decays. Predictions for the branching fractions of the semileptonic $B$ decays to radially ($2S$ and $3S$) and orbitally ($1P$ and $2P$) excited light mesons are given. Comparison with the previous calculations is performed. It is found that several decays to the excited light mesons have branching fractions of the order $10^{-4}$ and, thus, they can be measured at existing and future $B$ factories.

hep-ph↗

arXiv2025

Composite nature of exotic states from data analysis

We introduce two basic concepts: the compositeness for resonance and the Castillejo-Dalitz-Dyson (CDD) pole. Applying them to hadron states $X(3872)$, $Z_b(10610)$ and $Z_b(10650)$, and $T_{cc}$, we obtain their compositeness values and achieve deeper insights into their inner structure.

hep-ph↗

arXiv2025

Composite nature of the $T_{cc}$ state

In 2021, LHCb collaboration reported a very narrow state in the $D^0D^0π^+$ mass spectrum just below the $D^{*+}D^0$ mass threshold. We consider the influence of the Castillejo-Dalitz-Dyson (CDD) pole in the scattering amplitude to derive a general treatment for the two-body final state interaction near its threshold. The line shape (or the energy dependent event distribution) are then obtained, where the parameters can be fixed by fitting to the experimental data on the $D^0D^0π^+$ mass spectrum. Within our method the data are quite well reproduced. The pole structure in the complex energy plane indicates that the $T_{cc}$ state has a large portion of elementary degree of freedom (e.g., the compact tetraquark component) inside its hadron wave function. The compositeness as a measure of molecule component in its wave function is predicted to be $0.23_{-0.09}^{+0.40}$. Clearly, the non-molecular component takes a non-negligible or even dominant portion.

hep-ph↗

arXiv2025

Nature of X(3872) from recent BESIII data: Considering the universal feature of an S-wave threshold resonance

We analyze the recent data from the BESIII collaboration on the $X(3872)$ state in the $J/ψπ^+π^-$ and $D^0\bar{D}^0π^0$ decay channels. The quantum number and mass of the $X(3872)$ state allow us to exploit the universal feature of the very near-threshold $D\bar D^*$ scattering in the $S$ wave. The analysis of $J/ψπ^+π^-$ data and $D^0\bar{D}^0π^0$ data separately as well as the combined analysis of these data together, all support the conclusion that $X(3872)$ is an extremely weakly bound charm meson molecule.

hep-ph↗

arXiv2025

CP violation studies at Super Tau-Charm Facility

Charge-parity ($C\!P$) violation in the tau-charm energy region is a promising area for sensitive tests of Standard Model (SM) predictions and searches for new, beyond the SM physics. A future Tau-Charm Facility that operates at center-of-mass energies between 2.0 and 7.0 GeV, with a peak luminosity of $0.5\times10^{35}$~cm$^{-2}$s$^{-1}$, would provide huge numbers of hadrons and tau ($τ$) leptons that are produced in low-background environments and with well understood kinematic properties. In this report, prospects for unique studies of $C\!P$ violation in the decay of charmed hadrons, and in the production and decay of hyperons and $τ$ leptons at a next-generation tau-charm facility are discussed. In addition, opportunities for improved tests of $CPT$ invariance test in $K^{0}-\bar{K}^{0}$ mixing are presented.

hep-ex↗

arXiv2024

Unveiling the Structure of Hidden-Bottom Strange Pentaquarks via Magnetic Moments

Motivated by the discovery of hidden-charm strange pentaquarks, we conduct a systematic study of the magnetic moments of the hidden-bottom strange pentaquarks in molecular picture. We calculate magnetic moments of hidden-bottom strange pentaquarks with strangeness-1 and 2. Magnetic moment gives valuable information about the inner structure and shape of the hadron. The obtained results may be helpful to determine the inner structure of these new yet hypothetical states.

hep-ph↗

arXiv2023

Nature of $X(3872)$ from its radiative decay

We study the radiative decay of $X(3872)$ based on the assumption that $X(3872)$ is regarded as a $c\overline{c}$ charmonium with quantum number $J^{PC}=1^{++}$ ($J,\,P,\,C$ represent the spin, parity and charge conjugation, respectively). The form factors of $X(3872)$ transitions to $J/ψγ$ and $ψ'γ$ ($ψ'$ denotes $ψ(2S)$ throughout the paper) are calculated in the framework of the covariant light-front quark model. The phenomenological wave function of a meson depends on the parameter $β$, whose inverse essentially describes the confinement scale. In the present work, the parameters $β$ for the vector $J/ψ$ and $ψ'$ mesons will be determined through their decay constants, which are obtained from the experimental values of their partial decay widths to the electron-positron pair. For $X(3872)$, we determined the value of $β$ by the decay width of $X(3872)\rightarrow ψ'γ$. Then, we examined the width of $X(3872)\to J/ψγ$ in a manner of parameter-free prediction and compared it with the experimental value. As a result, an inconsistency or contradiction occurs between the widths of $X(3872)\to J/ψγ$ and $X(3872)\to ψ'γ$. We thus conclude that $X(3872)$ cannot be a pure $c\overline c$ resonance and that other components are necessary in its wave function.

hep-ph↗

arXiv2023

New insights into the oscillation of the nucleon electromagnetic form factors

The electromagnetic form factors of the proton and the neutron in the timelike region are investigated. Electron-positron annihilation into antinucleon-nucleon ($\bar NN$) pairs is treated in distorted wave Born approximation, including the final-state interaction in the $\bar NN$ system. The latter is obtained by a Lippmann-Schwinger equation for $\bar{N}N$ potentials derived within SU(3) chiral effective field theory. By fitting to the phase shifts and (differential) cross section data, a high quality description is achieved. With these amplitudes, the oscillations of the electromagnetic form factors of the proton and the neutron are studied. It is found that each of them can be described by two fractional oscillators. One is characterized as \lq overdamped' and dominates near the threshold, while the other is \lq underdamped' and plays an important role in the high-energy region. These two oscillators are essential to understand the distributions of polarized electric charges induced by hard photons for the nucleons.

nucl-th↗

arXiv2023

Two-body nonleptonic decays of the heavy mesons in the factorization approach

In the framework of the factorization approach we calculate the branching fractions of 100 two-body nonleptonic decay channels in total, including 44 channels of the charm meson decays and 56 channels of the bottom meson decays. For charm meson decays, we test and confirm the previous observation that taking the limit for the number of colors $N\to\infty$ significantly improves theoretical predictions. For bottom meson decays, the penguin contributions are included in addition. As an essential input, we employ the weak decay form factors obtained in the framework of the relativistic quark model based on the quasi-potential approach. These form factors have well been tested by calculating observables in the semileptonic $D$ and $B$ meson decays and confronting obtained results with experimental data. In general, the predictions for the nonleptonic decay branching fractions are acceptable. However, for a quantitative calculation it is necessary to account for a more subtle effects of the final-state interaction.

hep-ph↗

arXiv2022

Relativistic description of the semileptonic decays of bottom mesons

The form factors of the semileptonic $B$, $B_s$ and $B_c$ meson decays are calculated in the framework of the relativistic quark model based on the quasipotential approach in QCD. They are expressed through the overlap integrals of the meson wave function. All relativistic effects are consistently taken into account. The momentum transfer $q^2$ behavior of form factors is determined in the whole accessible kinematical range. We do not use any extrapolations, heavy quark $1/m_Q$ expansion or model assumptions about the shape of form factors. Convenient analytic expressions of the form factors are given, which very accurately reproduce the numerical results of our calculation. On the basis of these form factors and helicity formalism, the differential and total branching fractions of various semileptonic decays of bottom meson are calculated. The mean values of the forward-backward asymmetry $\langle A_{FB}\rangle$, lepton-side convexity parameter $\langle C^\ell_{F}\rangle$, longitudinal $\langle P^\ell_{L}\rangle$ and transverse $\langle P^\ell_{T}\rangle$ polarization of the charged lepton, and the longitudinal polarization fraction $\langle F_{L}\rangle$ for final-state vector meson are also evaluated. We present a detailed comparison of the obtained predictions with the calculations based on the covariant light-front quark model and confront them to available lattice QCD and experimental data. It is found that although both models predict close values of the total branching fractions, the differential distributions and forward-backward asymmetry and polarization parameters differ significantly, especially for the heavy-to-light semileptonic decays. We identify observables which measurement can help to discriminate between models.

hep-ph↗

arXiv2022

Composite nature of $Z_b$ states from data analysis

We use a near-threshold parameterization with explicit inclusion of the Castillejo-Dalitz-Dyson poles, which is more general than the effective range expansion, to study the bottomonium-like states $Z_b(10610)$ and $Z_b(10650)$. In terms of the partial-wave amplitude, we fit the event number distribution of $B^{(*)}\bar B^*$ system to the experimental data for these resonances from Belle Collaboration. The data could be described very well in our method, which supports the molecular interpretation. Then the relevant physical quantities are obtained, including the $B^{(*)}\bar{B}^*$ scattering length ($a$), effective range ($r$), and residue squared ($γ_s^2$) of the pole in the complex plane. In particular, we find the compositeness can range from about 0.4 up to 1 for the $B\bar B^*$ ($B^*\bar B^*$) component in the resonance $Z_b(10610)$ ($Z_b(10650)$).

hep-ph↗

arXiv2022

Analysis on the composite nature of the light scalar mesons $f_{0}(980)$ and $a_0(980)$

We study the weight or compositeness of the $ππ$-$K\bar{K}$ and $πη$-$K\bar{K}$ in the composition of the $f_0(980)$ and $a_0(980)$ resonances, respectively. Either we use the saturation of the total width and compositeness, or we use a Flatté parameterization taking also into account the spectral function of a near-threshold resonance. We make connections and compare between these two methods. We take input values for the pole mass and width from several determinations in the literature. In addition, we take as third input either the total compositeness or the decay-width branching ratio to the lighter channel for each resonance. It turns out that for the poles considered the meson-meson components are dominant for the $f_0(980)$, while for the $a_0(980)$ resonance they are subdominant. We also provide partial decay widths and partial compositeness coefficients, so that the $K\bar{K}$ component is the most important one for the $f_0(980)$. Additionally, this study stresses the need to distinguish between the bare and dressed couplings and widths in a Flatté parameterization. We elaborate on the connection between the partial-decay widths calculated in terms of the dressed couplings and the actual measured ones. Due to the coupled-channel dynamics when the pole lies near the heavier threshold in the second Riemann sheet some changes are needed with respect to standard relations.

hep-ph↗

arXiv2022

Revising inelastic dark matter direct detection by including the cosmic ray acceleration

The null signal from collider and dark matter (DM) direct detector experiments makes the interaction between DM and visible matter too small to reproduce the correct relic density for many thermal DM models. The remaining parameter space indicates that two almost degenerated states in the dark sector, the inelastic DM scenario, can co-annihilate in the early universe to produce the correct relic density. Regarding the direct detection of the inelastic DM scenario, the virialized DM component from the nearby halo is nonrelativistic and not able to excite the DM ground state, even if the relevant couplings can be considerable. Thus, a DM with a large mass splitting can evade traditional virialized DM direct detection. In this study, we connect the concept of cosmic-ray accelerated DM in our Milky Way and the direct detection of inelastic scattering in underground detectors to explore spectra that result from several interaction types of the inelastic DM. We find that the mass splitting $δ<\mathcal{O}(1~{\rm MeV})$ can still be reachable for cosmic ray accelerated DM with mass range $1~{\rm MeV}<m_{χ_1}<100~{\rm GeV}$ and sub-GeV light mediator using the latest PandaX-4T data, even though we conservatively use the astrophysical parameter (effective length) $D_{\rm eff}=1$ kpc.

hep-ph↗

arXiv2022

Pole analysis on the doubly charmed meson in $D^0D^0π^+$ mass spectrum

In this paper we study the scattering amplitudes of $D^{0}D^{0}π^+$-$D^{*+}D^{0}$ coupled channels based on $K$-matrix within the Chew-Mandelstam formalism. The $D^{0}D^{0}π^{+}$ invariant mass spectrum of LHCb is fitted and the pole parameters of the $T_{cc}^+$ are extracted. The analysis of pole behavior suggests that the $T_{cc}^+$ may originate from a $D^{*+}D^{0}$ virtual state and is formed as a result of an interplay between an attractive interaction between $D^0$ and $D^{*+}$ and coupling to $D^{0}D^0π^+$ channel.

hep-ph↗

arXiv2021

Possible Assignment of Excited Light $^3S_1$ Vector Mesons

We reanalyze the problems in the assignment of 3$^3S_1$ and 4$^3S_1$ light mesons, which have not yet been well established with the $q\bar{q}$ quark model. Regge trajectories and the $^3P_0$ decay model are used respectively to study the mass and width of the observed states and predict the missing ones. By comparing our calculations with the latest experiments, we suggest that the inconsistent data of $ρ(2150)$ may include two similar structures $ρ(4^3S_1)$ and $ω(4^3S_1)$. In addition, the problem of the $K^*(2^3S_1)$ assignment, with two observed states $K^*(1410)$ and $K^*(1680)$, is investigated, with several possible explanations.

hep-ph↗

arXiv2021

A comprehensive study on the semileptonic decay of heavy flavor mesons

The semileptonic decay of heavy flavor mesons offers a clean environment for extraction of the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements, which describes the CP-violating and flavor changing process in the Standard Model. The involved form factors where the dynamical information is encoded play an essential role in achieving any conclusive statement. That is, the knowledge of the form factors should be under good control, requiring one to examine more observables in addition to the branching fraction. In this paper, we provide the mean value and the $q^2$-dependent shape for further observables [differential decay distribution ($dΓ/dq^2$), forward-backward asymmetry ($\mathcal{A}_{FB}^l$), longitudinal ($P_L^l$) and transverse ($P_T^l$) polarization of a charged lepton, longitudinal polarization of a vector meson in the final state ($F_L^l(V)$), leptonic convexity parameter ($C_F^l$), and trigonometric moments ($W_i^l$) in the decay of $D_{(s)}$ and $B_{(s)}$ to $P/V l^+ ν_l$ ($l=e$, $μ$ or $τ$)], based on the predictions of the relevant form factors from the covariant light-front quark model. $P$ and $V$ denote the pseudoscalar and vector meson, respectively. As a comparison, we find a good agreement with the results from the covariant confining quark model and the relativistic quark model in the literature. As it has been observed that the $P_L^l$ and $F_L^l(V)$ are crucial quantities to discriminate various New Physics models, the reexamination of these observables from a different method is also essential and necessary.

hep-ph↗