The exclusive semileptonic decay form factors and widths of $B_c$ meson in the $c\bar c\ (η_c,J/ψ)$ states based on heavy quark effective theory are computed. The spectroscopic parameters of $B_c$ and the $c\bar c$ states deduced using the phenomenological coulomb plus power form of the $q-\bar q$ potential $(CPP_ν)$ with power index $ν$ have been employed to compute the Isgur wise function as well as the decay form factors. The universal behaviour of the Isgur-wise function at the maximum momentum transfer has been observed for different choices of $ν$ between 0.5 to 2.0. However, such an universality is not observed for the choice of $ν<0.5$. Our predictions for the branching ratio $B_c\rightarrowη_c\ell^+ν_\ell$ lie 0.50 $%$ - 0.56 $%$ while that for $B_c\rightarrow J/ψ\ell^+ν_\ell$ lie 1.8 $%$ - 2.0 $%$ for the choice of the potential index in the range $0.5\leqν\leq2.0$.
We present a detailed analysis of exclusive semileptonic decays of Bc meson involving pseudoscalar and vector mesons in the BSW framework, by investigating the effects of the flavor dependence on the average transverse quark momentum inside a meson. Branching ratios of exclusive semileptonic decays of Bc meson are predicted.
In this work, using the covariant light front approach with conventional vertex functions, we estimate the production rates of $D$-wave charmed/charmed-strange mesons via $B_{(s)}$ semileptonic decays. Due to these calculated considerable production rates, it is possible to experimentally search for $D$-wave charmed/charmed-strange mesons via the semileptonic decays, which may provide extra approach to explore $D$-wave charmed/charmed-strange mesons.
We investigate the semileptonic and nonleptonic decays of $B_s$ mesons. We work within the context of nonrelativistic constituent quark models. We calculate the different form factors that parameterize the hadron matrix elements.
Since the degree of polarization of the vector particle in semileptonic decay strongly influences the decay width of the particles, it can be used as a measure of CKM matrix elements. We show that |V_{cb}| can be determined from the measurement of polarization of vector meson in B,B_c --> V l nu decay, where $V$ is vector meson.
We investigate the effects of R-parity violation on the semileptonic decays of B-meson in the minimal supersymmetric standard model with explicit R-parity violation and discuss its physical implications. We find that the semileptonic decays of B-meson can be largely affected by the R-parity violation.
B meson semileptonic decays are a crucial tool in our studies of the quark mixing parameters Vcb and Vub. The interplay between experimental and theoretical challenges to achieve precision in the determination of these fundamental parameters is discussed.
Exclusive semileptonic $B$ decays into excited charmed mesons are studied with QCD sum rules in the leading order of heavy quark effective theory. Two universal Isgur-Wise functions τand ζfor semileptonic B decays into four lowest lying excited $D$ mesons ($D_1$, $D_2^*$, $D'_0$, and $D'_1$) are determined. The decay rates and branching ratios for these processes are calculated.
We obtain the wave function of mesonic systems interacting via a Cornell potential by applying improved variational approach. We study Isgur-Wise function and its parameters. Then we report our calculations on the parameters of semileptonic decay of B and Bs mesons. B-->D*l$nu$ process is also investigated in this work.
Consequences of the interference between external and internal spectator amplitudes for the lifetimes and semileptonic decay fractions of $B^0$ and $B^+$ mesons are discussed. Extrapolating from the constructive interference observed in 11 exclusive hadronic $B$ decays we find an inclusive semileptonic decay fraction of $(11.2 \pm 0.5 \pm 1.7)$\%, significantly closer to the experimental results than previous predictions.
We present a new charged Higgs search technique using the effects of scalar dynamics in semileptonic meson decay. Applying this method to a modest sample of B meson decays yields sensitivity to the high tan(beta) region well beyond existing charged Higgs searches. We present a new charged Higgs search technique using the effects of scalar dynamics in semileptonic meson decay. Applying this method to a modest sample of B meson decays yields sensitivity to the high tan(beta) region well beyond existing charged Higgs searches.
We review semi-inclusive charmless B decays, focussing on threshold logarithmic resumming and on universality of QCD dynamics in radiative and semileptonic decays.
We study the semileptonic branching fraction of $B$-meson into higher resonance of charmed meson $D^{**}$ by using the Bjorken sum rule and the heavy quark effective theory(HQET). This sum rule and the current experiment of $B$-meson semileptonic decay into $D$ and $D^*$ predict that the branching ratio into $D^{**}lν_l$ is about 1.7\%. This predicted value is larger than the value obtained by the various theoretical hadron models based on the HQET.
In this paper we consider the bilocal field approach for $QCD$. We obtain a bilocal effective meson action with a potential kernel given in relativistic covariant form. The corresponding Schwinger--Dyson and Bethe--Salpeter equations are investigated in detail. By introducing weak interactions into the theory we study heavy meson properties as decay constants and semileptonic decay amplitudes. Thereby, the transition from the bilocal field description to the heavy quark effective theory is discussed. Considering as example the semileptonic decay of a pseudoscalar $B$--meson into a pseudoscalar…
Exclusive semileptonic B meson decays to orbitally excited D mesons are investigated in the infinitely heavy quark limit in the framework of the relativistic quark model based on the quasipotential approach. The B\to D^{**}eνIsgur-Wise functions τ_{3/2}(w) and τ_{1/2}(w) are determined. It is found that the relativistic transformation of the meson wave functions (Wigner rotation of the light quark spin) contribute already at the leading order of the heavy quark expansion.
Within the framework of covariant confined quark model, we compute the transition form factors of $D$ and $D_s$ mesons decaying to light scalar mesons $f_0(980)$ and $a_0(980)$. The transition form factors are then utilized to compute the semileptonic branching fractions. We study the channels namely, $D_{(s)}^+ \to f_0(980) \ell^+ ν_\ell$ and $D \to a_0(980) \ell^+ ν_\ell$ for $\ell = e$ and $μ$. For computation of semileptonic branching fractions, we consider the $a_0(980)$ meson to be the conventional quark-antiquark structure and the $f_0(980)$ meson as the admixture of $s\bar{s}$ and ligh…
By using a constituent quark model we compute the form factors relevant to semileptonic transitions of B mesons into low-lying p-wave charmed mesons. We evaluate the q^2 dependence of these form factors and compare them with other model calculations. The Isgur-Wise functions tau(1/2) and tau(3/2) are also obtained in the heavy quark limit of our results.
Semileptonic decays of D-mesons into scalar hadronic states are investigated. Two extreme cases are considered: a) the meson decays directly into an uncorrelated scalar state of two two mesons and b) the decay proceeds via resonance formation. QCD sum rules including instanton contributions are used to calculate total and differential decay rates under the two assumptions.
Consequences of the interference between spectator amplitudes for the lifetimes and semileptonic decay fractions of B^0 and B^+ mesons are discussed. Assuming duality and constructive interference between spectator amplitudes we are able to explain the low experimental value for the semileptonic decay fraction of $B$ mesons. Extracting these amplitudes from a fit to 11 exclusive hadronic B decay fractions we find a_1 = 1.05 +/- 0.03 +/- 0.10, a_2 =+0.227 +/ 0.012 +/- 0.022, an inclusive semileptonic decay fraction of (11.2 +/- 0.5 +/- 1.7), and a lifetime ratio tau(B^+) / tau(B^0) = 0.83 +/- 0…
The form factors of the weak currents, which appear in the semileptonic decays of the heavy pseudoscalar mesons, are calculated within the quark confinement model by taking into account, for the first time, the structure of heavy meson vertex and the finite quark mass contribution in the heavy quark propagators. The results are in quite good agreement with the experimental data.
We analyze charm meson semileptonic $D \to V l ν_l$ and $D\to P l ν_l$ and nonleptonic $D \to P V$, $D \to PP$ and $D \to VV$ decays within a model which combines the heavy quark effective Lagrangian and chiral perturbation theory.
In the framework of a QCD relativistic potential model we evaluate the form factors describing the exclusive decays B => πl nu and B => K l+ l-. The present calculation extends a previous analysis of B meson decays into light vector mesons. We find results in agreement with the data, when available, and with the theoretical constraints imposed by the Callan-Treiman relation and the infinite heavy quark mass limit.
The transition form factors of (D_s -> f_0 l nu), (D -> f_0 l nu) and (B_u -> f_0 l nu) decays are calculated in 3-point QCD sum rule method, assuming that "f_0" is a quark-antiquark state with a mixture of strange and light quarks. The branching ratios of these decays are calculated in terms of the mixing angle.
We present the predictions of ISGW2, an update of the ISGW quark model for semileptonic meson decays. The updated model incorporates a number of features which should make it more reliable, including the constraints imposed by Heavy Quark Symmetry, hyperfine distortions of wavefunctions, and form factors with more realistic high recoil behaviors.
Using the (modified) MIT bag model we calculated formfactors and decay widths for pseudoscalar - pseudoscalar and pseudoscalar - vector semileptonic decays of heavy to light mesons. We discuss the physical phenomena which are important in these processes and their influence on the measurable quantities. Our results are consistent with the available experimental data. A comparison with the results of other models is also given.
This talk is a short review on the theoretical issues and uncertainties in the calculation of partial decay rates in inclusive B decays. The main emphasis is on charmless semileptonic decays, the B -> X(s) gamma photon spectrum, and the extraction of Vub using model-independent methods.
Using quasipotential approach, we have studied exclusive semileptonic decays of heavy mesons with the account of relativistic effects. Due to more complete relativistic description of the $s$ quark more precise expressions for semileptonic form factors are obtained. Various differential distributions in exclusive semileptonic decays of heavy mesons are calculated. It is argued that consistent account of relativistic effects and HQET motivated choice of the parameters of quark-antiquark potential allow to get reliable value for the ratio $A_2(0)/A_1(0)$ in the $D\to K^*lν_l$ decay as well as th…
The non-factorizable terms in the operator product expansion have been recognized as one of theoretical obstacles for precision determination of the mixing parameter $V_{ub}$ from semileptonic B decays. It is pointed out here that the recent CLEO data on the parameters of the heavy quark expansion $λ_1$ and ${\bar Λ}$, combined with a theoretical bound on $λ_1$ strongly favor the existence of a sizeable contribution of non-factorizable terms in semileptonic decays of $D$ mesons. Thus these terms are likely to solve the long-standing problem of the deficit of semileptonic decay rate of the $D$ …
We employ the relativistic constituent quark model to give a unified description of the leptonic and semileptonic decays of pseudoscalar mesons (π, K, D, D_s, B, B_s). The calculated leptonic decay constants and form factors are found to be in good agreement with available experimental data and other approaches. We reproduce the results of spin-flavor symmetry in the heavy quark limit.
Because quarks in hadronic states are subjected to strong QCD forces, it is not straight-forward to apply calculation obtained at the quark level to physical processes involving hadrons. In this paper we present a new approach to treat the semileptonic decays of pseudoscalar mesons. At the quark level, the process is straightforward. However, when we fold the quark-level process to the meson decay process, the complication from QCD effects come in. We make the fundamental assumption that the vertex of type M-q-qbar can be approximated by an effective constant gamma-5 coupling. With this assump…
In this paper we compute, within in the context of a relativistic quark model, the Isgur-Wise functions for exclusive semileptonic $\bar B \to X_c$ decays, where $X_c$ is any charmed mesons with total spin $J=0,1,2$ or one of their first excited states. The relevant matrix elements are computed by a direct numerical integration, in coordinate space, of the convolution of the wave function of the $B$ meson at rest and the wave function of the $X_c$ meson, boosted according with its recoil factor. Our results are compared with other predictions found in the existing literature.
In the extended $U(3)\times U(3)$ NJL model, semileptonic decays of $ρ$, $ω$, $ϕ$, $η$ and $η'$ mesons in both the ground and first radially excited states are described. Quark loops of the anomalous type are considered, which are based on the vertex $η\to VV$. The obtained results are in satisfactory agreement with the existing experimental data. In addition, a number of predictions for experimentally unmeasured decays of radially excited mesons are presented.
The evaluation, systematic analysis and numerical study of the semileptonic $τ$-lepton decays with two mesons in the final state has been made in the frame of the standard model extended by right handed neutrinos. In the analysis, heavy-neutrino nondecoupling effects, finite quark masses, quark and meson mixings, finite widths of vector mesons, chiral symmetry breakings in vector-meson--pseudoscalar-meson vertices and effective Higgs-boson--pseudoscalar-meson couplings have been included. Numerical estimates reveal that the decays $τ^-\to e^-π^-π^+$, $τ^-\to e^-K^-K^+$ and $τ^-\to e^-K^0\bar{K…
We study the inclusive semileptonic B decays in the parton model. The model gives a decay spectrum which is in excellent agreement with experiment and makes several predictions to be tested in the forseeable future.
We study exclusive nonleptonic and semileptonic decays of the Bc-meson within a relativistic constituent quark model previously developed by us. For the nonleptonic decays we use the factorizing approximation. We update our model parameters by using new experimental data for the mass and the lifetime of the Bc meson and the leptonic decay constants of the D-meson. We calculate the branching ratios for a large set of exclusive nonleptonic and semileptonic decays of the $B_c$ meson and compare our results with the results of other studies. As a guide for further experimental exploration we provi…
We evaluate semileptonic and two--meson nonleptonic decays of the $B_c^-$ meson in the framework of a nonrelativistic quark model. The former are done in spectator approximation using one--body current operators at the quark level. Our model reproduces the constraints of heavy quark spin symmetry obtained in the limit of infinite heavy quark mass. For the two--meson nonleptonic decays we work in factorization approximation. We compare our results to the ones obtained in different relativistic approaches.
The parton model for semileptonic B meson decays is studied with special attention to the decay distributions. We find that the spectra show dramatic variations when we introduce cuts on the hadronic energy or invariant mass of hadrons. Results for both $b\rightarrow u$ and $b\rightarrow c$ decays are presented. The detailed spectra may help to separate the two types of decays.
In the framework of the heavy quark effective theory, the leading order Isgur-Wise functions relevant to semileptonic decays of the orbitally $P$-wave excited $B_{s}$ meson states $B^{**}_{s}$, including the newly found narrow $B_{s1}(5830)$ and $B^{*}_{s2}(5840)$ states, into the ($D_{s1}(2536)$, $D^{*}_{s2}(2573)$) doublet are calculated from QCD sum rules. With these universal form factors, the decay rates and branching ratios are also estimated.
Exclusive semileptonic B decays to the lightest excited charmed mesons are investigated at order $Λ_{QCD}/m_Q$ in the heavy quark effective theory. At zero recoil, $Λ_{QCD}/m_Q$ corrections to the matrix elements of the weak currents can be written in terms of the leading Isgur-Wise functions for the corresponding transition and meson mass splittings. The differential decay rates are predicted, including $Λ_{QCD}/m_Q$ corrections with some model dependence away from zero recoil. Applications to B decay sum rules and factorization are presented.
Exclusive semileptonic B decays to orbitally and radially excited charmed mesons are investigated in the first order of the heavy quark expansion. The emerging leading and subleading Isgur-Wise functions are calculated in the framework of the relativistic quark model. It is found that both relativistic and the 1/m_Q corrections play an important role and substantially modify results. An interesting interplay between different corrections is observed.
We study the heavy quark effective theory prediction for semileptonic $B$ decays into an orbital excited $F$-wave charmed doublet, the ($2^{+}$, $3^{+}$) states ($D^{*'}_{2}$, $D_{3}$), at the leading order of heavy quark expansion. The corresponding universal form factor is estimated by using the QCD sum rule method. The decay rates we predict are $Γ_{B\to D^{*'}_{2}\ell\overlineν}=1.85\times10^{-19} {GeV}$ and $Γ_{B\to D_{3}\ell\overlineν}=1.78\times10^{-19} {GeV}$. The branching ratios are $\mathcal {B}(B\to D_{2}^{*'}\ell\overlineν)=4.6\times10^{-7}$ and $\mathcal {B}(B\to D_{3}\ell\overli…
A relativistic constituent quark model is adopted to give an unified description of the leptonic and semileptonic decays of pseudoscalar mesons (π, K, D, D_s, B, B_s). The calculated leptonic decay constants and form factors are found to be in good agreement with available experimental data and the results of other approaches. Eventually, the model is found to reproduce the scaling behaviours of spin-flavor symmetry in the heavy-quark limit.
The semileptonic $B_s (B) \to K_2^*(a_2, f_2) \ellν$, $\ell=τ, μ$ transitions are investigated in the frame work of the three-point QCD sum rules. Considering the quark condensate contributions, the relevant form factors of these transitions are estimated. The branching ratios of these channel modes are also calculated and compared with the obtained data for other approaches.
Taking into account the two-gluon condensate contributions, the transition form factors enrolled to the low energy effective Hamiltonian describing the semileptonic $χ_{b0}\rightarrow B_{c}\ell\barν, (\ell=(e,μ,τ))$ decay channel are calculated within three-point QCD sum rules. The fit function of the form factors then are used to estimate the decay width of the decay mode under consideration.
The branching ratios of the semileptonic decay widths of the charm mesons are analyzed, using three different models for the Isgur-Wise functions, such as ${D^0} \to {K^ - }{l^ + }\upsilon $, ${D^0} \to {π^ - }{l^ + }ν$, ${D_s} \to {K^0}{l^ + }ν$ and ${D_s} \to η{l^ + }ν$, where the form factors of these decays are discussed. The mass spectra of the charm mesons are obtained. We use a potential quark model and consider the non-relativistic Hamiltonian of the charm meson as a bound state of the quark-antiquark system. We take into account the harmonic-type confinement and also Hellmann potentia…
Semileptonic $B$ meson decays into the four lightest excited charmed meson states ($D_0^*$, $D_1^*$, $D_1$, and $D_2^*$) and their counterparts with $s$ quarks are investigated, including the full lepton mass dependence. We derive the standard model predictions for the differential branching fractions, as well as predictions for the ratios of the semi-tauonic and light lepton semileptonic branching fractions. These can be systematically improved using future measurements of the total or differential semileptonic rates to $e$ and $μ$, as well as the two-body hadronic branching fractions with a …
Recently, the BESIII collaboration has reported numerous measurements of various $D_{(s)}$ meson semileptonic decays with significantly improved precision. Together with similar studies carried out at BABAR, Belle, and CLEO, new windows to a better understanding of weak and strong interactions in the charm sector have been opened. In light of new experimental data, we review the theoretical description and predictions for the semileptonic decays of $D_{(s)}$ to a pseudoscalar or a vector meson. This review is essentially an extended discussion of our recently published results obtained in the …
We present the first complete results for the semileptonic and rare radiative form factors of B-mesons weak decay into a light vector-meson (rho, omega, K*, phi) in the light-cone sum-rule approach. The calculation includes radiative corrections, higher-twist corrections and SU(3)-breaking effects. The theoretical uncertainty is investigated in detail. A simple parametrization of the form factors is given in terms of three parameters each. We find that the form factors observe several relations inspired by heavy-quark symmetry.
The transition form factors of the semileptonic $B \rightarrow D_2^*(2460)\ell\barν\,\,\,\,(\ell=τ,μ,e)$ decay channel are calculated within the framework of the three-point QCD sum rules. The fit functions of the form factors are then used to estimate the total decay width and branching ratio of this transition. The order of branching ratio shows that this channel can be detected at LHCb.
The effects of spectator light quark in decays of heavy mesons are considered, which vanish in the limit of factorization of matrix elements of four-quark operators over the mesons. These effects include the difference of the total widths as well as of the semileptonic decay rates between the D^0 and D_s mesons and also a contribution to inclusive semileptonic decay rates of B^0 and B^\pm into the channel X_u l nu related to determination of the weak mixing parameter V_{ub}. If the observed difference of the lifetimes between D_s and D^0 mesons is attributed to non-factorizable terms, such ter…
I review the QCD sum rules calculations of the form factors governing the semileptonic decays of charmed and beauty mesons. In particular, I discuss the predicted dependence of the various form factors on $q^2$ and how it can be obtained for the form factors of vector and axial currents. In some cases the $q^2$ dependence, computed by QCD sum rules, is different from the outcome of lattice QCD. A Tau-Charm factory could be an efficient tool to study this aspect of the charmed meson transitions.
We present the semileptonic decay of $B_{c}$ meson in a QCD potential model with the coulombic part of the Cornell potential $-\frac{4α_{S}}{3r}+br+c$ as perturbation. Computing the slope and curvature of Isgur Wise function in this approach, we study the pseudoscalar and vector form factors for the transition of $B_{c}$ meson to its S wave charmonium $c\bar{c}$ states. Numerical estimates of widths for the transitions of $B_{c}\rightarrow J/ψ(η_{c})lν_{l}$ are presented. The results are found to be in good agreement with other theoretical values.
The anomalous value of the tensor form factor in the kaon decay K -> pi e nu and the destructive interference in pion decay pi -> e nu gamma can be simultaneously described by admixture of a tensor interaction in the standard V-A one. It is shown that the same tensor interaction can describe recent HERA data at very large Q^2.
We analyze the rare semileptonic $B_s \to (η, η') l^+ l^-$, $(l=e, μ, τ)$ and $B_s \to (η, η') ν\barν$ transitions probing the $\bar s s$ content of the $η$ and $η'$ mesons via three--point QCD sum rules. We calculate responsible form factors for these transitions in full theory. Using the obtained form factors, we also estimate the related branching fractions and longitudinal lepton polarization asymmetries. Our results are in a good consistency with the predictions of the other existing nonperturbative approaches.
We study the exclusive semileptonic decays B_s->D_{s0}^*\ell\barνand B_s->D_{s1}^*\ell\barν, where p-wave excited D_{s0}^* and D_{s1}^* states are identified with the newly observed D_{sJ}(2317) and D_{sJ}(2460) states. Within the framework of HQET the Isgur-Wise functions up to the subleading order of the heavy quark expansion are calculated by QCD sum rules. The decay rates and branching ratios are computed with the inclusion of the order of 1/m_Q corrections. We point out that the investigation of the B_s semileptonic decays to excited D_s mesons may provide some information about the natur…
We calculate the radiative corrections to the nonleptonic inclusive B decay mode $b\to c ud$ taking into account the charm quark mass. The corrections increase the decay rate by (4--8)\%, depending on the renormalization point. Using these results, we obtain an improved theoretical prediction for the semileptonic branching ratio of B mesons. This talk relies on work done in collaboration with E. Bagan, V.M.\ Braun and P. Gosdzinsky.
The form factors of semileptonic $B_{(s)}\to a_{1}(K_1)\, \ell^{+}\ell^{-}$, $ \ell=τ,μ,e$ transitions are investigated in the framework of the light-cone sum rules with $B$-meson distribution amplitudes, which play an important role in exclusive $B$ decays. The $B$-meson distribution amplitudes, $φ_{\pm}(ω)$ are a model-dependent form, so we consider four different parameterizations which can provide a reasonable description of $φ_{\pm}(ω)$ from QCD corrections. The branching fractions of these transitions are calculated. For a better analysis, a comparison of our results with the prediction …
The exclusive semileptonic $B\to π(ρ) eν$ decays are studied in the framework of the relativistic quark model based on the quasipotential approach in quantum field theory. The large recoil momentum of the final $π(ρ)$ meson allows for the expansion of the decay form factors at $q^2=0$ in the inverse powers of $b$-quark mass. This considerably simplifies the analysis of these decays. The $1/m_b$ expansion is carried out up to the first order. It is found that the $q^2$-dependence of the axial form factor $A_1$ is different from the $q^2$-behaviour of other form factors. We find $Γ(B\to πeν)=(3.…
The apparent gap between the measured and the expected value for the semileptonic branching ratio of $B$ mesons has become more serious over the last year. This is due to the improved quality of the data and to the increasing maturity of the theoretical treatment of non-perturbative corrections. We discuss various theoretical options to reduce the semileptonic $B$ branching ratio; among the more spectacular resolutions of the apparent puzzle is the possibility of an unorthodox enhancement in non-perturbative corrections or even of an intervention by `New Physics'. Phenomenological implications…
