Isgur-Wise Form Factor Research Articles

The benefits of $ \bar{B} \to {\bar{K}^*}{l^{+} }{l^{-} } $ decays at low recoil

Using the heavy quark effective theory framework put forward by Grinstein and Pirjol we work out predictions for \( \bar{B} \to {\bar{K}^*}{l^{+} }{l^{-} } \), l = e, μ, decays for a softly recoiling \( {\bar{K}^*} \), i.e., for large dilepton masses \( \sqrt {{{q^2}}} \) of the order of the b-quark mass m b . We work to lowest order in Λ/Q, where \( Q = \left( {{m_b}\sqrt {{{q^2}}} } \right) \) and include the next-to-leading order corrections from the charm quark mass m c and the strong coupling at \( \mathcal{O}\left( {{{{m_c^2}} \left/ {{{Q^2},{\alpha_s}}} \right.}} \right) \). The leading Λ/m b corrections are parametrically suppressed. The improved Isgur-Wise form factor relations correlate the \( \bar{B} \to {\bar{K}^*}{l^{+} }{l^{-} } \) transversity amplitudes, which simplifies the description of the various decay observables and provides opportunities for the extraction of the electroweak short distance couplings. We propose new angular observables which have very small hadronic uncertainties. We exploit existing data on \( \bar{B} \to {\bar{K}^*}{l^{+} }{l^{-} } \) distributions and show that the low recoil region provides powerful additional information to the large recoil one. We find disjoint best-fit solutions, which include the Standard Model, but also beyond-the-Standard Model ones. This ambiguity can be accessed with future precision measurements.

SemileptonicBq→Dq*lν(q=s,d,u)decays in QCD sum rules

The form factors relevant to ${B}_{q}\ensuremath{\rightarrow}{D}_{q}^{*}({J}^{P}={1}^{\ensuremath{-}})\ensuremath{\ell}\ensuremath{\nu}$ ($q=s$, $d$, $u$) decays are calculated in the framework of the three point QCD sum rules approach. The heavy quark effective theory prediction of the form factors as well as $1/{m}_{b}$ corrections to those form factors are obtained. A comparison of the results for the ratio of form factors at zero recoil limit and other values of ${q}^{2}$ with the predictions of the subleading Isgur-Wise form factor application for $B\ensuremath{\rightarrow}{D}^{*}\ensuremath{\ell}\ensuremath{\nu}$ is presented. The total decay width and branching ratio for these decays are also evaluated using the ${q}^{2}$ dependencies of these form factors. The results are in good agreement with the constituent quark meson model and existing experimental data. The $q=s$ case can also be detected at LHC in the near future.

DecaysB¯→D**πand the Isgur-Wise functionsτ1/2(w),τ3/2(w)

We perform a phenomenological analysis of the decays $B \to D^{**}\pi$, where $D^{**}$ is a $P$-wave excited meson with total angular momentum $j = {1 \over 2}$ or ${3 \over 2}$ for the light cloud, recently measured by the Belle Collaboration in the modes $\bar{B}^0\to D^{**+}\pi^-$ (Class I) and $B^- \to D^{**0}\pi^-$ (Class III). Making the reasonable assumption of naive factorization, that we test in $B \to D(D^*)\pi$ decays, Class I decays allow to extract the Isgur-Wise form factors $\tau_{1/2}(w)$, $\tau_{3/2}(w)$ at $w \cong w_{max}$ ($q^2 \cong 0$). We obtain $\tau_{1/2}(w_{max}) < 0.20$, $\tau_{3/2}(w_{max}) = 0.31 \pm 0.12$. We discuss the question of the $w$ dependence of these IW functions. We find agreement with the Bakamjian-Thomas quark model of form factors and, extrapolating at $w=1$, with Bjorken and Uraltsev sum rules. We discuss also Class III decays, where the $D^{**0}$ $(j = {1 \over 2})$ emission diagram contributes. We extract the corresponding $f_{D_{1/2}}$ decay constant, that is in agreement with theoretical estimates at finite mass. Finally, we must warn that $1/m_Q$ corrections could be large and upset the results of the present stage of this analysis. On the other hand, we confront present data on the semileptonic rate of $B$ mesons to excited states with theoretical expectations.

Lattice renormalization of the static quark derivative operator

We give the analytical expressions and the numerical values of radiative corrections to the covariant derivative operator on the static quark line, used for the lattice calculation of the Isgur–Wise form factors τ1/2(1) and τ3/2(1). These corrections induce an enhancement of renormalized quantities if an hypercubic blocking procedure is used for the Wilson line, while there is a reduction without such a procedure.

Lattice measurement of the Isgur–Wise functions [formula omitted] and [formula omitted

We propose a method to compute the Isgur–Wise form factors τ1/2(1) and τ3/2(1) for the decay of B mesons into orbitally excited (P wave) D** charmed mesons on the lattice in the static limit. We also present the result of a quenched exploratory numerical simulation which shows that the signal/noise ratio allows for a more dedicated computation.

Subleading Isgur–Wise function of Λb→Λc1 using QCD sum rules

Subleading Isgur–Wise form factor τ(v·v′) at O(1/mQ) for Λb→Λc11/2,3/2 weak transition is calculated by using the QCD sum rules in the framework of the heavy quark effective theory (HQET), where Λ1/2c1 and Λ3/2c1 are the orbitally excited charmed baryon doublet with JP=(1−/2,3−/2). We consider the subleading contributions from the weak current matching in the HQET. The interpolating currents with transverse covariant derivative are adopted for Λ1/2c1 and Λ3/2c1 in the analysis. The slope parameter ρ2 in linear approximation of τ is obtained to be ρ2=2.76 and the interception to be τ(1)=−1.27 GeV.

A study of heavy-light mesons on the transverse lattice

We present results from a first study of B-mesons that is based on a transverse lattice formulation of light-front QCD. The shape of the Isgur-Wise form factor is in very good agreement with experimental data. However, the calculations yield rather large values for f B and Λ compared to contemporary calculations based on other techniques.

B mesons on the transverse lattice

We present results from a first study of $B$-mesons that is based on a transverse lattice formulation of light-front QCD. The shape of the Isgur-Wise form factor is in very good agreement with experimental data. However, the calculations yield rather large values for $f_B$ and $\bar{\Lambda}$ compared to contemporary calculations based on other techniques.

Study of heavy-light mesons on the transverse lattice

We present results from a study of meson spectra and structure in the limit where one quark is infinitely heavy. The calculations, based on the framework of light-front QCD formulated on a transverse lattice, are the first non-perturbative studies of B mesons in light-front QCD. We calculate the Isgur-Wise form factor, light-cone distribution amplitude, the heavy-quark parton distribution function and the leptonic decay constant of B mesons.

Factorization in color-favored B-meson decays to charm

Improved $B$ meson decay data have permitted more incisive tests of factorization predictions. A concurrent benefit is the ability to constrain the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cb}|$. Using a simultaneous fit to differential distributions $d \Gamma(\ob \to D^{*+} l^- \bar \nu_l)/ dq^2$ measured by the CLEO and LEP Collaborations, the rates for the color-favored decays $\ob \to D^{(*)+} (\pi^-,\rho^-,a_1^-)$, and the rate for $\ob \to D^+ l^- \bar \nu_l$, we find $|V_{cb}| = 0.0415 \pm 0.0022$. The slope of the universal Isgur-Wise form factor is described by a parameter found to be $\rs = 1.52 \pm 0.11$. Taking the $D_s$ meson decay constant from the world average of direct measurements, we predict satisfactorily the branching ratios for $\ob \to D^{(*)+} D_s^{(*)-}$. Ratios of helicity amplitudes for color-favored processes are also found to be in accord with predictions.

Measurement of V from the decay process →Dℓ

A new precise measurement of |V_{cb}| and of the branching ratio BR(\bar{B^0} -> D^{*+} \ell^- \bar{\nu_\ell}) has been performed using a sample of about 5000 semileptonic decays \bar{B^0} -> D^{*+} \ell^- \bar{\nu_\ell}, selected by the DELPHI detector at LEP I by tagging the soft pion from D^{*+} -> D^0 \pi^+. The results are: V_{cb}=(39.0 +/- 1.5 (stat.) ^{+2.5}_{-2.6} (syst. exp.) +/- 1.3 (syst. th.)) x 10^{-3} BR(\bar{B^0} -> D^{*+} \ell^- \bar{\nu_\ell})=(4.70 +/- 0.13 (stat.) ^{+0.36}_{-0.31} (syst. exp.))% The analytic dependences of the differential cross-section and of the Isgur Wise form factor as functions of the variable w = v_{B^0}.v_{D^*} have also been obtained by unfolding the experimental resolution.

Leading Isgur–Wise form factor of Λb→ Λc1 transition using QCD sum rules

The leading Isgur–Wise form factor ξ( y) parametrizing the semileptonic transitions Λ b→Λ 1/2 c1ℓ ν ̄ and Λ b→Λ 3/2 c1ℓ ν ̄ is calculated by using the QCD sum rules in the framework of heavy quark effective theory, where Λ 1/2 c1 and Λ 3/2 c1 is the orbitally excited charmed baryon doublet with J P =(1 −/2,3 −/2). The interpolating currents with transverse covariant derivative are adopted for Λ 1/2 c1 and Λ 3/2 c1 in the analysis. The slope parameter ρ 2 in linear approximation of the Isgur–Wise function is obtained to be ρ 2=2.01, and the interception to be ξ(1)=0.29. The decay branching ratios are estimated.

Analysis of theΛb→Λc+lν¯ldecay within a light-front constituent quark model

We present an investigation of the Isgur-Wise form factor relevant for the semileptonic decay Lambda_b -> \Lambda_c + l nu_l performed within a light-front constituent quark model. Adopting different baryon wave functions it is found that the Isgur-Wise form factor depends sensitively on the baryon structure. It is shown however that the shape of the Isgur-Wise function in the full recoil range relevant for the Lambda_b -> \Lambda_c + l nu_l decay can be effectively constrained using recent lattice QCD results at low recoil. Then, the Lambda_b -> \Lambda_c + l nu_l decay is investigated including both radiative effects and first-order power corrections in the inverse heavy-quark mass. Our final predictions for the exclusive semileptonic branching ratio, the longitudinal and transverse asymmetries, and the longitudinal to transverse decay ratio are: Br(Lambda_b -> \Lambda_c + l nu_l) = (6.3 +/- 1.6) % |V_bc / 0.040|**2 ~ tau(Lambda_b) / (1.24 ps), a_L = -0.945 +/- 0.014, a_T = -0.62 +/- 0.09 and R_L/T = 1.57 +/- 0.15, respectively. Moreover, both the longitudinal asymmetry and the (partially integrated) longitudinal to transverse decay ratio are found to be only marginally affected by the model dependence of the Isgur-Wise form factor as well as by first-order power corrections; therefore, their experimental determination might be a very interesting tool for testing the SM and for investigating possible New Physics.

SemileptonicB→ρandB→a1transitions in a quark-meson model

We evaluate the form factors governing the exclusive decays B->rho l nu, B->a_1 l nu, by using an effective quark-meson lagrangian. The model is based on meson-quark interactions, and the computation of the mesonic transition amplitudes is performed by considering diagrams with heavy mesons attached to loops containing heavy and light constituent quarks. This approach was successfully employed to compute the Isgur-Wise form factors and other hadronic observables for negative and positive parity heavy mesons and is presently used for exclusive heavy-to-light weak transitions. We also evaluate a few strong coupling constants appearing in chiral effective lagrangians for heavy and light mesons.

Universal Isgur-Wise form factors from QCD sum rules in HQET

We review the role of the universal Isgur-Wise functions parameterizing the B meson semileptonic matrix elements to excited charm states in the infinite heavy quark mass limit. We also discuss the determination of such form factors by QCD sum rules in the framework of the Heavy Quark Effective Theory.

Isgur-Wise form factors of heavy baryons within a light-front constituent quark model

The space-like elastic form factors of baryons containing a heavy quark are investigated within a light-front constituent quark model in the limit of infinite heavy-quark mass, adopting a gaussian-like ansatz for the three-quark wave function. The results obtained for the Isgur-Wise form factors corresponding both to a spin-0 and a spin-1 light spectator pair are presented. It is found that the Isgur-Wise functions depend strongly on the baryon structure, being sharply different in case of diquark-like or collinear-type configurations in the three-quark system. It is also shown that the relativistic effects lead to a saturation property of the form factors as a function of the baryon size. Our results are compared with those of different models as well as with recent predictions from QCD sum rules and lattice QCD simulations; the latter ones seem to suggest the dominance of collinear-type configurations, in which the heavy-quark is sitting close to the center-of-mass of the light quark pair.

Exclusive and inclusive weak decays of the B-meson

A relativistic quark model is applied to the description of semileptonic and non-leptonic charmed decays of the B-meson. The exclusive semileptonic modes B → D lve and → D ∗ lve are described through the universal Isgur-Wise form factor, which is calculated in terms of a constituent quark model wave function for the B-meson. Different approximations for the latter, either based on a phenomenological ansatz or derived from analyses of the meson spectra, are adopted. In particular, two wave functions, constructed via the Hamiltonian light-front formalism using a relativized and a non-relativistic constituent quark model, are considered, obtaining a link between standard spectroscopic quark models and the B-meson decay physics. The inclusive semileptonic and non-leptonic branching ratios are calculated within a convolution approach, inspired by the partonic model and involving the same B-meson wave function used for the evaluation of the exclusive semileptonic modes. Our results for the major branching ratios are consistent with available experimental data and the sum of all the calculated branching ratios turns out to be close to unity. In particular, we found that (i) a remarkable fraction (∼ 35%) of semileptonic decay modes occur in non- D, non- D ∗ final states; (ii) non-perturbative effects enhance the inclusive b → c ud decay channels, with a sizable contribution provided by internal decays into heavy mesons and baryon-antibaryon pairs; the resulting reduction of the semileptonic branching ratio brings the theoretical prediction in agreement with the experimental value without increasing at the same time the charm counting.

Comment on "Semileptonic meson decays in the quark model: An update"

The usefulness of this quark model is uncertain because it seriously underestimates the transition rate to excited states in semileptonic $B$ decays. The Isgur-Wise form factor which fits experiment suppresses the decay rate to $D$ plus ${D}^{*}$ by about 40% but only about 7% out of 40% is restored via decays to excited states. Experiment and a heavy-quark theory analysis by Falk, Luke, and Savage suggest that much more should show up in excited states.

Large Nc universality of the baryon Isgur-Wise form factor: The group theoretical approach.

In a previous article, it has been proved under the framework of chiral soliton model that the same Isgur--Wise form factor describes the semileptonic $\Lambda_b\to\Lambda_c$ and $\Sigma^{(*)}_b\to\Sigma^{(*)}_c$ decays in the large $N_c$ limit. It is shown here that this result is in fact independent of the chiral soliton model and is solely the consequence of the spin-flavor SU(4) symmetry which arises in the baryon sector in the large $N_c$ limit.

Heavy-Quark Limit in a Relativistic Quark-Confinement Model

We have studied the weak decay constants and the Isgur-Wise form factors of the B and D mesons in the heavy-quark limit by employing a relativistic 2quark-confinement model. It is an attempt to improve our previous work within the same line of thinking, but by incorporating a couple of novel aspects. First, the infrared behaviour of the heavy quark is considered by modifying its conventional propagator in terms of a single parameter ν. Second, the mass difference between the heavy meson and heavy quark E = m H – M Q has been included. It is found that the weak decay constants depend strongly on this mass difference E with a relatively mild ν dependence. As for the Isgur-Wise function it is controlled more sensitively by the infrared parameter ν, leading to its suppression at maximum meson recoil.