Covariant Light-front Approach Research Articles

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.

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.

Insights into the nature of X(3872) through B meson decays* *Supported by the National Natural Science Foundation of China (11347030) and the Program of Science and Technology Innovation Talents in Universities of Henan Province (14HASTIT037)

We study the decays in the perturbative QCD (PQCD) approach, involving the puzzling resonance , where P represents a light pseudoscalar meson (K or π). Assuming to be a charmonium state, we obtain the following results. (a) The branching ratios of the and decays are consistent with the results predicted by the covariant light-front approach within errors; however, they are larger than those given by the generalized factorization approach. (b) The branching ratio of the decay is predicted as , which is smaller than the previous PQCD calculation result but still slightly larger than the upper limits set by Belle and BaBar. Hence, we suggest that the decays should be precisely measured by the LHCb and Belle II experiments to help probe the inner structure of . (c) Compared with the decays, the decays have significantly smaller branching ratios, which drop to values as low as . (d) The direct CP violations of these considered decays are small () because the penguin contributions are loop suppressed compared to the tree contributions. The mixing-induced CP violation of the decay is highly consistent with the current world average value %. Experimentally testing the results for the branching ratios and CP violations, including the implicit and isospin symmetries of these decays, helps probe the nature of .

Study of Bu,d,s→K0*(1430)P and K0*(1430)V decays within QCD factorization

We study the nonleptonic charmless ${B}_{u,d,s}\ensuremath{\rightarrow}{K}_{0}^{*}(1430)P$ ($P=K$, $\ensuremath{\pi}$) and ${K}_{0}^{*}(1430)V$ $(V={K}^{*},\ensuremath{\rho},\ensuremath{\omega},\ensuremath{\phi})$ decays. The amplitudes are calculated within the QCD factorization, and the nonperturbative quantities are evaluated by using a covariant light-front approach. The branching fractions and $CP$ asymmetries of theses decay modes are calculated, some decay modes are first predicted, and some useful relations based on $SU(3)$ flavor symmetry are discussed. Comparing the theoretical results with the current available experimental data, it is found that ${K}_{0}^{*}(1430)$ can be described as the lowest-lying p-wave $(s,u/d)$ state rather than the first excited one.

Estimating the production rates of D -wave charmed mesons via the semileptonic decays of bottom mesons * * Supported by the National Natural Science Foundation of China (11222547, 11175073, 11647301), the National Program for Support of Top-notch Young Professionals and the Fundamental Research Funds for the Central Universities

Using the covariant light-front approach with conventional vertex functions, we estimate the production rates of D -wave charmed/charmed-strange mesons via the semileptonic decays. As the calculated production rates are significant, it seems possible to experimentally search for D -wave charmed/charmed-strange mesons via semileptonic decays, which may provide an additional approach for exploring D -wave charmed/charmed-strange mesons.

Radiative D(D s ) decays in the covariant light front approach

In the covariant light-front quark model, we investigate the D→V,A,T tensor form factors induced by c→u transition, which can contribute to radiative D(D s ) decays. The short distance contribution is much smaller than the experimental data, thus radiative D(D s ) decays is dominated by nonperturbative effect. We also include the weak annihilation contributions and the long distance contributions to D→Vγ. Our results for D→(K ∗0,ϕ)γ decays can approach the data and the other predictions should be checked with the BEPCII experiment.

Nonleptonic two-body charmlessBdecays involving a tensor meson in the perturbative QCD approach

Two-body charmless hadronic B decays involving a light tensor meson in the final states are studied in the perturbative QCD approach based on $k_T$ factorization. From our calculations, we find that the decay branching ratios for color allowed tree-dominated decays $B\to a_{2}^{0}\pi^{+}$ and $B\to a_{2}^{-}\pi^{+}$ modes are of order $10^{-6}$ and $10^{-5}$, respectively. While other color suppressed tree-dominated decays have very small branching ratios. In general, the branching ratios of most decays are in the range of $10^{-5}$ to $10^{-8}$, which are bigger by one or two orders of magnitude than those predictions obtained in Isgur-Scora-Grinstein-Wise II model and in the covariant light-front approach, but consistent with the recent experimental measurements and the QCD factorization calculations. Since the decays with a tensor meson emitted from vacuum are prohibited in naive factorization, the contributions of nonfactorizable and annihilation diagrams are very important to these decays, which are calculable in our perturbative QCD approach. We also give predictions to the direct CP asymmetries, some of which are large enough for the future experiments to measure. Because we considered the mixing between $f_{2}$ and $f_{2}'$, the decay rates are enhanced significantly for some decays involving $f_{2}^{\prime}$ meson, even with a small mixing angle.

Form Factors of Few-Body Systems: Point Form Versus Front Form

We present a relativistic point-form approach for the calculation of electroweak form factors of few-body bound states that leads to results which resemble those obtained within the covariant light-front formalism of Carbonell et al. (Phys. Rep. 300:215–347, 1998). Our starting points are the physical processes in which such form factors are measured, i.e. electron scattering off the bound state, or the semileptonic weak decay of the bound state. These processes are treated by means of a coupled-channel framework for a Bakamjian–Thomas type mass operator. A current with the correct covariance properties is then derived from the pertinent leading-order electroweak scattering or decay amplitude. As it turns out, the electromagnetic current is affected by unphysical contributions which can be traced back to wrong cluster properties inherent in the Bakamjian–Thomas construction. These spurious contributions, however, can be separated uniquely, as in the covariant light-front approach. In this way we end up with form factors which agree with those obtained from the covariant light-front approach. As an example we will present results for electroweak form factors of heavy–light systems and discuss the heavy-quark limit which leads to the famous Isgur–Wise function.

Erratum:B→V,A,Ttensor form factors in the covariant light-front approach: Implications on radiativeBdecays [Phys. Rev. D81, 114006 (2010)

We reanalyze the $B\to M$ tensor form factors in a covariant light-front quark model, where $M$ represents a vector meson $V$, an axial-vector meson $A$, or a tensor meson $T$. The treatment of masses and mixing angles in the $K_{1A,1B}$ systems is improved, where $K_{1A}$ and $K_{1B}$ are the $^3P_1$ and $^1P_1$ states of the axial-vector meson $K_1$, respectively. Rates of $B\to M\gamma$ decays are then calculated using the QCD factorization approach. The updated $B\to K^*\gamma$, $B\to K_1(1270)\gamma$, $K_1(1400)\gamma$ and $K_2\gamma$ rates agree with the data. The $K_1(1270)$--$K_1(1400)$ mixing angle is found to be about $51^\circ$. The sign of the mixing angle is fixed by the observed relative strength of $B\to K_1(1270)\gamma$ and $K_1(1400)\gamma$. The formalism is then applied to $B_s\to M$ tensor form factors. We find that the calculated $B_s\to \phi\gamma$ rate is consistent with experiment, though in the lower end of the data. The branching fractions of $B_s\to f_1(1420)\gamma$ and $f'_2(1525)\gamma$ are predicted to be of order $10^{-5}$ and it will be interesting to search for these modes. Rates on $B_s\to f_1(1285)\gamma$, $h_1(1380)\gamma$, $h_1(1170)\gamma$, $f_2(1270)\gamma$ decays are also predicted.

Formula omitted] and [formula omitted] form factors in covariant light-front approach

B→(π,η,η′) transition form factors are investigated in the covariant light-front approach. With theoretical uncertainties, we find that B→(π,η,η′) form factors at q2=0 are f+(π,η,η′)(0)=(0.245−0.001+0.000±0.011,0.220±0.009±0.009,0.180±0.008−0.007+0.008) for vector current and fT(π,η,η′)(0)=(0.239−0.003−0.018+0.002+0.020,0.211±0.009−0.015+0.017,0.173±0.007−0.013+0.014) for tensor current, respectively. With the obtained q2-dependent f+π(q2) and observed branching ratio (BR) for B¯d→π+ℓν¯ℓ, the Vub is found as |Vub|LF=(3.99±0.13)×10−3. As a result, the predicted BRs for B¯→(η,η′)ℓν¯ℓ decays with ℓ=e,μ are given by (0.49−0.04−0.07+0.02+0.10,0.24−0.02−0.03+0.01+0.04)×10−4, while the BRs for D−→(η,η′)ℓν¯ℓ are (11.1−0.6−0.9+0.5+0.9,1.79−0.08−0.12+0.07+0.12)×10−4. In addition, we also study the integrated lepton angular asymmetries for B¯→(π,η,η′)τν¯τ: (0.277−0.001−0.007+0.001+0.005,0.290−0.000−0.003+0.002+0.003,0.312−0.000−0.006+0.004+0.005).

Nonleptonic charmless two-body B → AT decays

In this work, we have studied hadronic charmless two-body B decays involving p-wave mesons in the final state. We have calculated branching ratios of B → AT decays (where A and T denote a 3P1 axial-vector and a tensor meson, respectively), using B → T form factors obtained in the covariant light-front (CLF) approach and the full effective Hamiltonian. We have obtained that , , (with f1 = f1(1285), f1(1420)) for , with , for where K1 = K1(1270), K1(1400). It seems that these decays can be measured in experiments at B factories. Additionally, we have found that and ratios could be useful to determine numerical values of mixing angles and , respectively.

Nonleptonic charmless two-body B decays involving tensor mesons in the covariant light-front approach

We reanalyzed nonleptonic charmless two-body B decays involving tensor mesons in the final state motivated by the disagreement between current experimental information and theoretical predictions obtained in the ISGW2 model for some (where P, V and T denote a pseudoscalar, a vector and a tensor meson, respectively). We have calculated branching ratios of charmless B → PT and B → VT modes, using B → T form factors obtained in the covariant light-front (CLF) approach and the full effective Hamiltonian. We have considered the η − η′ two-mixing angle formalism for B → η(′)T channels, which increases branching ratios for these processes. Our predictions obtained in the CLF approach are, in general, greater than those computed in the framework of the ISGW2 model and more favorable with the available experimental data. Specifically, our results for exclusive channels B → ηK*2(1430) and B → ϕK*2(1430) are in agreement with recent experimental information.

Study of Bc -→X(3872)π-(K-) decays in the covariant light-front approach

In the covariant light-front quark model, we calculate the form factors of Bc -→J/ψ and Bc -→X(3872). Since the factorization of the exclusive processes Bc -→J/ψπ-(K-) and Bc -→X(3872)π-(K-) can be proved in the soft-collinear effective theory, we can easily get the branching ratios for these decays from the form factors. Taking the uncertainties into account, our results for the branching ratio of Bc -→J/ψπ-(K-) are consistent with previous studies. By identifying X(3872) as a 1++ charmonium state, we obtain BR(Bc -→X(3872)π-)=(1.7+0.7+0.1+0.4 -0.6-0.2-0.4)×10-4 and BR(Bc -→X(3872)K-)=(1.3+0.5+0.1+0.3 -0.5-0.2-0.3)×10-5. Assuming X(3872) to be a 1– state, the branching ratios will be one order of magnitude larger than those of the 1++ state. These results can easily be used to test the charmonium description for this mysterious meson X(3872) at the LHCb experiment.

Covariant light-front approach for heavy quarkonium: decay constants, P → γγ and V → Pγ

The light-front approach is a relativistic quark model and offers many insights into the internal structures of the hadronic bound states. In this study, we apply the covariant light-front approach to ground-state heavy quarkonium. The pesudoscalar and vector meson decay constants are discussed. We present a detailed study of two-photon annihilation P → γγ and magnetic dipole transition V → Pγ processes. The numerical predictions of the light-front approach are consistent with the experimental data and those in other approaches. The relations of the light-front approach with the other methods are discussed in brief.

PARITY-EVEN AND PARITY-ODD MESONS IN COVARIANT LIGHT-FRONT APPROACH

Decay constants and form factors for parity-even (s-wave) and parity-odd (p-wave) mesons are studied within a covariant light-front approach. The three universal Isgur-Wise functions for heavy-to-heavy meson transitions are obtained.

Covariant light-front approach fors-wave andp-wave mesons: Its application to decay constants and form factors

We study the decay constants and form factors of the ground-state s-wave and low-lying p-wave mesons within a covariant light-front approach. Numerical results of the form factors for transitions between a heavy pseudoscalar meson and an s-wave or p-wave meson and their momentum dependence are presented in detail. In particular, form factors for heavy-to-light and B to D** transitions, where D** denotes generically a p-wave charmed meson, are compared with other model calculations. The experimental measurements of the decays B^- to D** pi^- and B to D D**_s are employed to test the decay constants of D**_s and the B to D** transition form factors. The heavy quark limit behavior of the decay constants and form factors is examined and it is found that the requirement of heavy quark symmetry is satisfied. The universal Isgur-Wise (IW) functions, one for s-wave to s-wave and two for s-wave to p-wave transitions, are obtained. The values of IW functions at zero recoil and their slope parameters can be used to test the Bjorken and Uraltsev sum rules.

Electromagnetic form factors in the light-front formalism and the Feynman triangle diagram: Spin-0 and spin-1 two-fermion systems

The connection between the Feynman triangle diagram and the light-front formalism for spin-0 and spin-1 two-fermion systems is analyzed. It is shown that in the limit ${q}^{+}=0$ the form factors for both spin-0 and spin-1 systems can be uniquely determined using only the good amplitudes, which are not affected by spurious effects related to the loss of rotational covariance present in the light-front formalism. At the same time, the unique feature of the suppression of the pair creation process is maintained. Therefore, a physically meaningful one-body approximation, in which all the constituents are on their mass shells, can be consistently formulated in the limit ${q}^{+}=0.$ Moreover, it is shown that the effects of the contact term arising from the instantaneous propagation of the active constituent can be canceled out from the triangle diagram by means of an appropriate choice of the off-shell behavior of the bound state vertices; this implies that in the case of good amplitudes the Feynman triangle diagram and the one-body light-front result match exactly. For illustrative purposes our covariant light-front approach is applied to the evaluation of the $\ensuremath{\rho}$-meson elastic form factors.

Deuteron electromagnetic form factors in the light-front dynamics

The deuteron form factors are calculated in the framework of the relativistic nucleon-meson dynamics, by means of the explicitly covariant light-front approach. The inflluence of the nucleon electromagnetic form factors is discussed. At Q2 < 3 (GeV/c)2 the prediction for the structure function A(Q2) and for the tensor polarization observable t20 are in agreement with the recent data of CEBAF/TJNAF.