Covariant Light-front Quark Model Research Articles

Imprinting New Physics by Using Angular Profiles of the Flavor-Changing-Neutral-Current Process Bc → Ds* (→ Dsπ) ℓ+ℓ-

Abstract The decays governed by the flavor-changing-neutral-current (FCNC) transitions, such as $b\rightarrow s\ell ^{+}\ell ^{-}$, provide an important tool to test the physics in and beyond the Standard Model (SM). This work focuses on investigating the FCNC process $B_{c}\rightarrow D_{s}^{*} \left(\rightarrow D_{s}\pi \right)\ell ^{+}\ell ^{-}(\ell =e,\mu ,\tau )$. Being an exclusive process, the initial and final state meson matrix elements involve the form factors, which are nonperturbative quantities and need to be calculated using specific models. By using the form factors calculated in the covariant light-front quark model, we analyze the branching fractions and angular observables such as the forward-backward asymmetry $A_{\mathrm{ FB}}$, polarization fractions (longitudinal and transverse) $F_{L(T)}$, CP asymmetry coefficients $A_{i}$, and CP-averaged angular coefficients $S_{i}$, both in the SM and in some new physics (NP) scenarios. Some of these physical observables are a potential source of finding the physics beyond the SM and help us to distinguish various NP scenarios.

Bc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varvec{B_c}$$\\end{document} to A transition form factors and semileptonic decays in self-consistent covariant light-front approach

We present a comprehensive analysis of the semileptonic weak decays of Bc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_c$$\\end{document} meson decaying to axial-vector (A) mesons for bottom-conserving and bottom-changing decay modes. We employ self-consistent covariant light-front quark model (CLF QM) that uses type-II correspondence to eliminate inconsistencies in the traditional type-I CLF QM. As a fresh attempt, we test the self-consistency in CLF QM through type-II correspondence for Bc→A\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_c \\rightarrow A$$\\end{document} meson transition form factors. We establish that in type-II correspondence the form factors for longitudinal and transverse polarization states are numerically equal and are free from zero-mode contributions, which confirms the self-consistency of type-II correspondence for Bc→A\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_c \\rightarrow A$$\\end{document} transition form factors. Furthermore, we ascertain that the problems of inconsistency and violation of covariance of CLF QM within the type-I correspondence are resolved in type-II correspondence for Bc→A\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_c \\rightarrow A$$\\end{document} transitions. We thoroughly investigate the effects of self-consistency between type-I and type-II schemes using a comparative analysis. In this investigation, we employ a direct calculation approach to determine the form factors within the space-like region. Subsequently, we employ a vector meson dominance (VMD)-inspired three-parameter form to extrapolate these form factors into the physically accessible region. This enables us to study the q2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$q^2$$\\end{document} dependence of the form factors in weak hadronic currents for the whole accessible kinematic range for both bottom-conserving as well as bottom-changing transitions. In addition, we extend our analysis to predict the branching ratios of the semileptonic weak decays of Bc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_c$$\\end{document} meson involving axial-vector meson in the final state to quantify the effects of self-consistency in these decays that were not studied before. We evaluate the lepton mass effect on these branching ratios and various other important physical observables, such as forward-backward asymmetries, lepton-side convexity parameter, asymmetry parameter, and longitudinal polarization asymmetries and fractions. Finally, we obtain the lepton flavor universality ratios for various decays.

Study of B(s) meson decays to D0*(2300) , Ds0*(2317) , Ds1(2460) and Ds1(2536) within the covariant light-front approach

In this work, we investigate the form factors of the transitions B(s)→D0*(2300),Ds0*(2317), Ds1(2460), and Ds1(2536) in the covariant light-front quark model (CLFQM), where these final states are considered as P-wave excited charmed mesons. In order to obtain the form factors for the physical transition processes, we extend these form factors from the spacelike region to the timelike region. The q2-dependence for each transition form factor is also plotted. Then, combined with those form factors, the branching ratios of the two-body nonleptonic decays B(s)→D(s)0*(2300,2317)M, Ds1(2460,2536)M with M being a light pseudoscalar (vector) meson or a charmed meson are calculated by considering the quantum chromodynamics (QCD) radiative corrections to the hadronic matrix elements within the QCD factorization approach. Most of our predictions are comparable to the results given by other theoretical approaches and the present available data. Published by the American Physical Society 2024

Heavy flavor conserved semi-leptonic decay of Bs in the covariant light-front approach

We study the heavy flavor conserved semi-leptonic decay Bs→Bℓν in the covariant light front approach. The covariant light front quark model is used to calculate the transition form factors of Bs→B(⁎) as well as Ds→D, which are consistent with the leading power predictions from the heavy quark symmetry. The angular distribution analysis on the Bs→B(⁎)lν¯ decay is performed by investigating the forward-backward asymmetry of the lepton. We also study the angular distribution of Bs→B⁎(→Bγ)lν¯ decay both through the lepton forward-backward asymmetry and the azimuth angle. The branching fractions of Bs→Blν¯ and Bs→B⁎lν¯ are at the order 10−8 and 10−9, respectively. The number of Bs→Blν¯ events is estimated to be 1.76. The branching fraction of Bs→B⁎(→Bγ)lν¯ is at the order 10−11, which is calculated by introducing Breit-Wigner distribution for the intermediate B⁎.

Semileptonic and nonleptonic weak decays of $$\psi (1S,2S)$$ and $$\eta _{c}(1S,2S)$$ to $$D_{(s)}$$ in the covariant light-front approach

AbstractIn addition to the strong and electromagnetic decay modes, the $$\psi (1S,2S)$$ ψ ( 1 S , 2 S ) and $$\eta _{c}(1S,2S)$$ η c ( 1 S , 2 S ) can also decay via the weak interaction. Such weak decays can be detected by the high-luminosity heavy-flavor experiments. At present, some of the semileptonic and nonleptonic $$J/\Psi $$ J / Ψ weak decays have been measured at BESIII. Researching for these charmonium weak decays to $$D_{(s)}$$ D ( s ) meson can provide a platform to check of the standard model (SM) and probe new physics (NP). So we investigate the semileptonic and nonleptonic weak decays of $$\psi (1S,2S)$$ ψ ( 1 S , 2 S ) and $$\eta _{c}(1S,2S)$$ η c ( 1 S , 2 S ) to $$D_{(s)}$$ D ( s ) within the covariant light-front quark model (CLFQM). With form factors of the transitions $$\psi (1S,2S)\rightarrow D_{(s)}$$ ψ ( 1 S , 2 S ) → D ( s ) and $$\eta _{c}(1S,2S)\rightarrow D_{(s)}$$ η c ( 1 S , 2 S ) → D ( s ) calculated under the CLFQM, we predict and discuss some physical observables, such as the branching ratios, the longitudinal polarizations $$f_{L}$$ f L and the forward–backward asymmetries $$A_{FB}$$ A FB . One can find that the Cabibbo-favored semi-leptonic decay channels $$\psi (1\,S,2\,S)\rightarrow D_{s}^{-}\ell ^{+}\nu _{\ell }$$ ψ ( 1 S , 2 S ) → D s - ℓ + ν ℓ with $$\ell =e,\mu $$ ℓ = e , μ and the nonleptonic decay modes $$\psi (1S,2S)\rightarrow D_{s}^{-}\rho ^{+}$$ ψ ( 1 S , 2 S ) → D s - ρ + have relatively large branching ratios of the order $$\mathcal {O}(10^{-9})$$ O ( 10 - 9 ) , which are most likely to be accessible at the future high-luminosity experiments.

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 cc‾ charmonium with quantum number JPC=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)→ψ′γ. Then, we examined the width of X(3872)→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)→J/ψγ and X(3872)→ψ′γ. We thus conclude that X(3872) cannot be a pure cc‾ resonance and that other components are necessary in its wave function.

Study of the nonleptonic charmless B→SS\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B \\rightarrow SS$$\\end{document} decays with the QCD factorization approach

Inspired by the brilliant prospects of the ongoing B meson experiments, the hadronic charmless B→\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\rightarrow }$$\\end{document}SS decays are studied by considering the next-to-leading (NLO) contributions with the QCD factorization approach, where S denotes the scalar mesons K0∗(1430)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$K_{0}^{*}(1430)$$\\end{document} and a0(1450)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$a_{0}(1450)$$\\end{document}. Branching ratios and CP violating asymmetries are estimated with the updated values of hadronic parameters obtained from a covariant light-front quark model, for two scenarios where the scalar mesons are the 13P0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1^{3}P_{0}$$\\end{document} and 23P0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$2^{3}P_{0}$$\\end{document} states. It is found that the NLO contributions are very important for the B→\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\rightarrow }$$\\end{document}SS decays. For the B→\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\rightarrow }$$\\end{document}a0(1450)K0∗(1430)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$a_{0}(1450)K_{0}^{*}(1430)$$\\end{document} and Bs\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_{s}$$\\end{document}→\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\rightarrow }$$\\end{document}K0∗(1430)K¯0∗(1430)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$K_{0}^{*}(1430)\\overline{K}_{0}^{*}(1430)$$\\end{document} decays, branching ratios can reach up to the order of O(10-5)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mathcal {O}}(10^{-5})$$\\end{document} by assuming that the scalar mesons are the 1P states, and should first be investigated in the future experiments.

Semileptonic decays B_{c} meson to S-wave charmonia and X(3872) within the covariant light-front approach

In this work, we investigate the semileptonic decays of B_{c} meson to eta _{c}(1S,2S,3S), psi (1S,2S,3S) and X(3872) within the framework of covariant light-front quark model (CLFQM). We combine the helicity amplitudes via the corresponding form factors to obtain the branching ratios of the semileptonic decays B_{c}rightarrow eta _{c}(1S, 2S, 3S)ell nu _{ell }, B_{c}rightarrow psi (1S, 2S, 3S))ell nu _{ell } and B_{c}rightarrow X(3872)ell nu _{ell }, with ell =e,mu ,tau . In view of the R_{J/Psi } anomaly released by the LHCb collaboration, it is necessary to systematically calculate the ratios R_X with X=psi (1S,2S,3S),eta _c(1S,2S,3S),X(3872), which are helpful for checking the lepton flavor universality (LFU). We also take into account another two physical observables, the longitudinal polarization fraction f_{L} and the forward–backward asymmetry A_{FB}, which can provide new clues for understanding the R_{J /Psi } anomaly. Such theoretical predictions are necessary and interesting, and can be tested in future LHCb experiments.

Covariant light-front approach for B_c decays into charmonium: implications on form factors and branching ratios

In this work, we investigate the form factors of B_c decays into J/Psi , psi (2S,3S),eta _c, eta _c(2,S,3,S), chi _{c0}, chi _{c1}, h_c, and X(3872) mesons in the covariant light-front quark model (CLFQM). For the purpose of the branching ratio calculation, the form factors of B_crightarrow D^{(*)}, D^{(*)}_s transitions are also included. In order to obtain the form factors for the physical transition processes, we need to extend these form factors from the space-like region to the time-like region. The q^2 dependence for each transition form factor is also plotted. Then, using the factorization method, we calculate the branching ratios of 80 B_c decay channels with a charmonium involved in each mode. Most of our predictions are comparable to the results given by other approaches. As to the decays with the radially excited-state S-wave charmonia involved, such as psi (2S,3S) and eta _c(2S,3S), two sets of parameters for their light-front wave functions, corresponding to scenario I (SI) and scenario II (SII), are adopted to calculate the branching ratios. By comparing with the future experimental data, one can discriminate which parameters are more favored.

Phenomenology analysis of bar{B}^* rightarrow V tau ^-bar{nu }_{tau } decays in and beyond the Standard Model

Motivated by the persistent anomalies reported in the brightarrow c tau bar{nu } data, we investigate the semileptonic decays bar{B}^* rightarrow V tau ^-bar{nu }_{tau } (V=D^*_{u,d,s},J/psi ), within the Standard Model and beyond. The relevant transition form factors, being calculated in the covariant light-front quark model, is the main source of theoretical uncertainties. Using various best-fit solutions for the new operator Wilson coefficients, we report numerical results on various observables related to the processes bar{B}^* rightarrow V tau ^-bar{nu }_{tau }, such as the branching ratios, the ratio of branching fractions, the hadron and lepton polarization asymmetries, the forward–backward asymmetries and the convexity parameter. We also predict the q^2 distribution of these observables both within the Standard Model and in various new physics scenarios. The accessible observables are studied in order to assess their sensitivity to the different new physics scenarios. We can find that some of the new physics scenarios can be differentiated from each other by using these observables and their correlations. We also find that some observables of these decay modes are sizeable and deviate significantly (for new physics coupling parameter S_R especially) from their corresponding standard model values, which are expected to be within the reach of Run III of Large Hadron Collider experiment. And experimental information on these distributions which will be testified in the future can help to disentangle the dynamical origin of the current anomalies.

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.

Two- and three-body hadronic decays of charmed mesons involving a tensor meson

We study the quasi-two-body $D\ensuremath{\rightarrow}TP$ decays and the three-body $D$ decays proceeding through intermediate tensor resonances, where $T$ and $P$ denote tensor and pseudoscalar mesons, respectively. We employ the $D\ensuremath{\rightarrow}T$ transition form factors based upon light cone sum rules and the covariant light-front quark model to evaluate the decay rates, with the former giving a better agreement with current data. Though the tree amplitudes with the emitted meson being a tensor meson vanish under factorization approximation, contributions proportional to the tensor decay constant ${f}_{T}$ can be produced from vertex and hard spectator-scattering corrections. We also investigate the finite-width effects of the tensor mesons and find that, contrary to three-body $B$ decays, the tensor-mediated $D$ decays are more seriously affected and the narrow width approximation has to be corrected. More experimental data are required in order to extract information topological amplitudes associated with quasi-two-body $D\ensuremath{\rightarrow}TP$ decays. Among the data, the ${D}^{+}\ensuremath{\rightarrow}{f}_{2}{\ensuremath{\pi}}^{+}$ and ${D}^{+}\ensuremath{\rightarrow}{\overline{K}}_{2}^{*0}{\ensuremath{\pi}}^{+}$ branching fractions are not self-consistent and further clarification is called for.

Weak decays * * Supported by the National Natural Science Foundation of China (11875122 and 11475055) and the Program for Innovative Research Team in University of Henan Province (19IRTSTHN018)

Motivated by the rapid development of heavy flavor physics experiments, we study the tree-dominated nonleptonic ( ) decays within the factorization approach. The relevant transition form factors are calculated by employing the covariant light-front quark model. Helicity amplitudes are calculated and analyzed in detail, and a very clear hierarchical structure is presented. The branching fractions are computed and discussed. Numerically, the CKM-favored and decays have relatively large branching fractions, , and could be observed by LHC and Belle-II experiments in the future.

Revisiting the form factors of Prightarrow 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 ({{mathcal {F}}}=g, a_{pm } and f) of Prightarrow 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 lambda =0 and ± 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 Mrightarrow M_0 relative to the traditional type-I scheme; meanwhile, the results of {{mathcal {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, i.e., [{{mathcal {F}}}]_{mathrm{SLF}}=[{{mathcal {F}}}]_{mathrm{val.}}doteq [{{mathcal {F}}}]_mathrm{full}. The numerical results for some Prightarrow 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.

Semileptonic and nonleptonic weak decays of Λb0

The recent experimental developments require a more precise theoretical study of weak decays of heavy baryon $\Lambda_b^0$. In this work, we provide an updated and systematic analysis of both the semi-leptonic and nonleptonic decays of $\Lambda^0_b$ into baryons $\Lambda^+_c$, $\Lambda$, $p$, and $n$. The diquark approximation is adopted so that the methods developed in the $B$ meson system can be extended into the baryon system. The baryon-to-baryon transition form factors are calculated in the framework of a covariant light-front quark model. The form factors $f_3, ~g_3$ can be extracted and are found to be non-negligible. The semi-leptonic processes of $\Lambda^0_b\to \Lambda^+_c(p)l^-\bar\nu_l$ are calculated and the results are consistent with the experiment. We study the non-leptonic processes within the QCD factorization approach. The decay amplitudes are calculated at the next-to-leading order in strong coupling constant $\alpha_s$. We calculate the non-leptonic decays of $\Lambda^0_b$ into a baryon and a s-wave meson (pseudoscalar or vector) including 44 processes in total. The branching ratios and direct CP asymmetries are predicted. The numerical results are compared to the experimental data and those in the other theoretical approaches. Our results show validity of the diquark approximation and application of QCD factorization approach into the heavy baryon system.

Predictions of decay observables in the standard model and beyond

We study Bc → (D, D*)τ ν semileptonic decays mediated via b → u τ ν charged current interactions using the Bc → (D, D*) transition form factors obtained in the covariant light front quark model. We give predictions on the branching ratios, ratio of branching ratios, and various asymmetries pertaining to these decay modes within the standard model and within various new physics scenarios. These results can be tested in the ongoing or in the future experiments and can provide complimentary information regarding the observed anomalies in B → τν, B → (D, D*)τν and Bc → J/Ψτν decays.

Self-consistency and covariance of light-front quark models: Testing via P , V , and A meson decay constants, and P→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.

Footprints of new physics in b→cτν transitions

In this work, we perform a combined analysis of the $R(D)$, $R(D^*)$, and $R(J/\psi)$ anomalies in a model-independent manner based on the general framework of the four-fermion effective field theory, paying special attention to the use of the hadronic form factors. For the $B\to D(D^*)$ transition form factors, we use the HQET parametrization that includes the higher order corrections of $\mathcal{O}(\alpha_s,\Lambda_{\mathrm{QCD}}/m_{b,c})$ and was determined recently from a fit to lattice QCD and light-cone sum rule results in complementary kinematical regions of the momentum transfer. For the $B_c\to J/\psi(\eta_c)$ transitions, we use the form factors calculated in the covariant light-front quark model, which are found to be well consistent with the preliminary lattice results. With this particular treatment of hadronic matrix elements, in our analysis the two classes of vector operators are shown to be the most favored single new physics (NP) operators by the current experimental constraints within $2\sigma$ and the LEP1 data on $Br(B_c\to \tau\nu)$ as well as the minimum $\chi^2$ fit, while the tensor operator is also allowed but severely constrained, and the scalar ones are excluded. Using the favored ranges and fitted values of the Wilson coefficients of the single NP operators, we also give a prognosis for the physical observables such as the ratios of decay rates ($R(D(D^*)), R(J/\psi(\eta_c))$) and other polarized observables as well as the $q^2$ distributions.

Semileptonic B and B_s decays involving scalar and axial-vector mesons

We report our theoretical calculations on the branching fractions for the semileptonic B and B_s decays based on the form factors in the covariant light-front quark model. That is, B (B_s) rightarrow (P,, V,, S,,A) ell nu _ell , where P and V denote the pseudoscalar and vector mesons, respectively, while S denotes the scalar meson with mass above 1 GeV and A the axial-vector meson. The branching fractions for the semileptonic Brightarrow P and V modes have been measured very well in experiment and our theoretical values are in good agreement with them. The ones for Brightarrow S and A modes are our theoretical predictions. There is little experimental information on the semileptonic B_s decays although much theoretical effort has been done. In addition, we predict the branching fractions of Brightarrow D^*_0(2400) ell bar{nu }_ell and B_srightarrow D^{*-}_{s0}(2317) ell bar{nu }_ell as (2.31pm 0.25)times 10^{-3} and (3.07pm 0.34)times 10^{-3}, in order, assuming them as the conventional mesons with quark-antiquark configuration. The high luminosity e^+e^- collider SuperKEKB/Belle-II is running, with the data sample enhanced by a factor of 40 compared to Belle, which will provide huge opportunity for the test of the theoretical predictions and further help understand the inner structure of these scalar and axial-vector mesons, e.g., the glueball content of f_0(1710) and the mixing angles for the axial-vector mesons. These decay channels can also be accessed by the LHCb experiment.

Branching fractions of semileptonic D and D_s decays from the covariant light-front quark model

Based on the predictions of the relevant form factors from the covariant light-front quark model, we show the branching fractions for the D (D_s) rightarrow (P,,S,,V,,A),ell nu _ell (ell =e or mu ) decays, where P denotes the pseudoscalar meson, S the scalar meson with a mass above 1 GeV, V the vector meson and A the axial-vector one. Comparison with the available experimental results are made, and we find an excellent agreement. The predictions for other decay modes can be tested in a charm factory, e.g., the BESIII detector. The future measurements will definitely further enrich our knowledge of the hadronic transition form factors as well as the inner structure of the even-parity mesons (S and A).