Heavy Quark Effective Theory Parameters Research Articles

Bayesian fit analysis to full distribution data of overline{mathrm{B}}to {mathrm{D}}^{left(ast right)}mathrm{ell}overline{nu }:left|{mathrm{V}}_{mathrm{cb}}right| determination and new physics constraints

We investigate the semi-leptonic decays of Bto {D}^{left(ast right)}mathrm{ell}overline{nu } in terms of the Heavy-Quark-Effective-Theory (HQET) parameterization for the form factors, which is described with the heavy quark expansion up to mathcal{O}left(1/{m}_c^2right) beyond the simple approximation considered in the original CLN parameterization. An analysis with this setup was first given in the literature, and then we extend it to the comprehensive analyses including (i) simultaneous fit of |Vcb| and the HQET parameters to available experimental full distribution data and theory constraints, and (ii) New Physics (NP) contributions of the V2 and T types, such as left(overline{c}{upgamma}^{mu }{P}_Rbright)left(overline{mathrm{ell}}{gamma}_{mu }{P}_Lnu mathrm{ell}right)kern0.5em mathrm{and}kern0.5em left(overline{c}{sigma}^{mu nu}{P}_Lbright)left(overline{mathrm{ell}}{sigma}_{mu nu}{P}_L{nu}_{mathrm{ell}}right) , to the decay distributions and rates. For this purpose, we perform Bayesian fit analyses by using Stan program, a state-of-the-art public platform for statistical computation. Then, we show that our |Vcb| fit results for the SM scenarios are close to the PDG combined average from the exclusive mode, and indicate significance of the angular distribution data. In turn, for the SM + NP scenarios, our fit analyses find that non-zero NP contribution is favored at the best fit point for both SM + V2 and SM + T depending on the HQET parameterization model. A key feature is then realized in the overline{B}to {D}^{left(ast right)}tau overline{nu} observables. Our fit result of the HQET parameters in the SM(+T) produces a consistent value for RD while smaller for {R}_{D^{ast }} , compared with the previous SM prediction in the HFLAV report. On the other hand, SM + V2 points to smaller and larger values for RD and {R}_{D^{ast }} than the SM predictions. In particular, the {R}_{D^{ast }} deviation from the experimental measurement becomes smaller, which could be interesting for future improvement on measurements at the Belle II experiment.

Parameters of heavy quark effective theory from N f = 2 lattice QCD

Abstract We report on a non-perturbative determination of the parameters of the lattice Heavy Quark Effective Theory (HQET) Lagrangian and of the time component of the heavy-light axial-vector current with N f = 2 flavors of massless dynamical quarks. The effective theory is considered at the 1/m h order, and the heavy mass m h covers a range from slightly above the charm to beyond the beauty region. These HQET parameters are needed to compute, for example, the b-quark mass, the heavy-light spectrum and decay constants in the static approximation and to order 1/m h in HQET. The determination of the parameters is done non-perturbatively. The computation reported in this paper uses the plaquette gauge action and two different static actions for the heavy quark described by HQET. For the light-quark action we choose non-perturbatively O(a)-improved Wilson fermions.

Operator product expansion for B-meson distribution amplitude and dimension-5 HQET operators

When the bilocal heavy-quark effective theory (HQET) operator for the B-meson distribution amplitude has a light-like distance t between the quark and antiquark fields, the scale ∼1/t separates the UV and IR regions, which induce the cusp singularity in radiative corrections and the mixing of multiparticle states in nonperturbative corrections, respectively. We treat these notorious UV and IR behaviors simultaneously using the operator product expansion, with the local operators of dimension d⩽5 and radiative corrections at order αs for the corresponding Wilson coefficients. The result is derived in the coordinate space, which manifests the Wilson coefficients with Sudakov-type double logarithms and the higher-dimensional operators with additional gluons. This result yields the B-meson distribution amplitude for t less than ∼1 GeV−1, in terms of Λ¯=mB−mb and the two additional HQET parameters as matrix elements of dimension-5 operators. The impact of these novel HQET parameters on the integral relevant to exclusive B decays, λB, is also discussed.

MOMENTS OF THE HADRONIC MASS DISTRIBUTION IN SEMILEPTONIC B MESON DECAYS

We present a measurement of the first and second moments of the squared-mass distribution of charm hadrons in semileptonic decays of B mesons based on ~ 180 pb-1 of data taken with the CDF II detector at the Fermilab Tevatron. For a minimum lepton momentum of 0.7 GeV/c in the B meson rest frame, we measure the first two moments of the D** → D(*)π component to be [Formula: see text] and [Formula: see text]. Combining these values with known contributions from the D and D* components, we obtain the overall charm hadron moments [Formula: see text] and [Formula: see text] where [Formula: see text] is the spin-averaged D meson mass and the subscript "BR" denotes the uncertainty from the branching ratios used to combine the D, D* and D** components. From these moments we also determine the non-perturbative Heavy Quark Effective Theory parameters Λ and λ1 in the pole and 1S mass schemes.

Measurement of the moments of the hadronic invariant mass distribution in semileptonicBdecays

Using 180 pb^-1 of data collected with the CDF II detector at the Tevatron, we measure the first two moments of the hadronic invariant mass-squared distribution in charmed semileptonic B decays. From these we determine the non-perturbative Heavy Quark Effective Theory parameters Lambda and lambda_1, used to relate the B meson semileptonic branching ratio to the CKM matrix element |V_cb|. For a minimum lepton momentum of 0.7 GeV/c in the B rest frame me measure the first two moments of the D** --> D(*) pi component to be <m^2_D**> = (5.83 +/- 0.16(stat) +/- 0.08(syst)) GeV^2, <(m^2_D** - <m^2_D**>)^2> = (1.30 +/- 0.69(stat) +/- 0.22(syst)) GeV^4. Combining these with the discrete mass terms from the D and D* mesons, we find the total moments to be <M^2_Xc> - mbar_D^2 = (0.467 +/- 0.038_(stat) +/- 0.068(syst)) GeV^2, <(M^2_Xc - <M^2_Xc>)^2> = (1.05 +/- 0.26(stat) +/- 0.13(syst)) GeV^4, where mbar_D is the spin-averaged D mass. The systematic error is dominated by the uncertainties in the world-average branching ratios used to combine the D, D* and D** contributions. The analysis makes no assumptions about the shape or resonant structure of the D** --> D(*) pi invariant mass distribution.

Nonperturbative determination of heavy meson bound states

In this paper we obtain a heavy meson bound state equation from the heavy quark equation of motion in heavy quark effective theory (HQET) and the heavy meson effective field theory we developed very recently. The bound state equation is a covariant extention of the light-front bound state equation for heavy mesons derived from light-front QCD and HQET. We determine the covariant heavy meson wave function variationally by minimizing the binding energy �. Subsequently the other basic HQET parameters �1 and �2, and the heavy quark masses mb and mc can also be consistently determined.

Phenomenological profiles of the inclusive hadron spectra in the decayB→Xsl+l−

Hadron spectra and hadronic moments in the decay $\stackrel{\ensuremath{\rightarrow}}{B}{X}_{s}{l}^{+}{l}^{\ensuremath{-}}$ are calculated taking into account both the short-distance and long-distance contributions in the decay amplitude using a Fermi motion (FM) model to incorporate the B-meson wave-function effects. The measured branching ratios for the inclusive decays $\stackrel{\ensuremath{\rightarrow}}{B}{X}_{s}+(J/\ensuremath{\psi},{\ensuremath{\psi}}^{\ensuremath{'}},\dots{})\ensuremath{\rightarrow}{X}_{s}{l}^{+}{l}^{\ensuremath{-}}$ are used to fix the normalization of the long-distance contribution. Assuming factorization, the momentum distribution of the $J/\ensuremath{\psi}$ measured by the CLEO Collaboration is fitted in the FM model which is then used to calculate the hadronic spectra from the resonant contribution also away from the $J/\ensuremath{\psi}$ resonance. We also study the effect of various descriptions of the resonant and nonresonant $c\overline{c}$ contributions in $\stackrel{\ensuremath{\rightarrow}}{B}{X}_{s}{l}^{+}{l}^{\ensuremath{-}}$ existing in the literature on the hadron energy and invariant mass spectra, and in the forward-backward asymmetry. Selective cuts on the hadron and dilepton invariant masses can be used to reduce the $B\overline{B}$ background and resonant contribution and, as an example, we work out the hadron spectra with the experimental cuts used by the CLEO Collaboration in searching for the decay $\stackrel{\ensuremath{\rightarrow}}{B}{X}_{s}{l}^{+}{l}^{\ensuremath{-}}$. We show that data from the forthcoming B facilities could be used effectively to measure the short-distance contribution in $\stackrel{\ensuremath{\rightarrow}}{B}{X}_{s}{l}^{+}{l}^{\ensuremath{-}},$ enabling precise determination of the FM model parameters as well as the heavy quark effective theory parameters ${\ensuremath{\lambda}}_{1}$ and $\overline{\ensuremath{\Lambda}}.$

Nonperturbative determination of heavy meson bound states

In this paper we obtain a heavy meson bound state equation from the heavy quark equation of motion in heavy quark effective theory (HQET) and the heavy meson effective field theory we developed very recently. The bound state equation is a covariant extention of the light-front bound state equation for heavy mesons derived from light-front QCD and HQET. We determine the covariant heavy meson wave function variationally by minimizing the binding energy $\bar{\Lambda}$. Subsequently the other basic HQET parameters $\lambda_1$ and $\lambda_2$, and the heavy quark masses $m_b$ and $m_c$ can also be consistently determined.

Motion of abquark inside aBmeson: The parton model versus the Altarelli-Cabibbo-Corbo-Maiani-Martinelli model

We study the distribution function of the $b$ quark for inclusive semileptonic $B$ decays in the framework of the parton model. We compare the functional behavior of the fragmentation inspired function and the Gaussian Altarelli-Cabibbo-Corbo-Maiani-Martinelli function, and discuss their validity. Using the heavy quark effective theory parameters, we can critically test these models.

Spectroscopy of heavy mesons expanded in1/mQ

Operating just once with the naive Foldy-Wouthuysen-Tani transformation on the relativistic Fermi-Yang equation for $Q\bar q$ bound states described by the semi-relativistic Hamiltonian which includes Coulomb-like as well as confining scalar potentials, we have calculated heavy meson mass spectra of D and B together with higher spin states. Based on the formulation recently proposed, their masses and wave functions are expanded up to the second order in $1/m_Q$ with a heavy quark mass $m_Q$ and the lowest order equation is examined carefully to obtain a complete set of eigenfunctions for the Schr\"odinger equation. Heavy quark effective theory parameters, $\bar\Lambda$, $\lambda_1$, and $\lambda_2$, are also determined at the first and second order in $1/m_Q$.