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Title: Lattice QCD results for the B --> D(*) l nu form factors: F(1) and G(1)

Abstract

I review the current status of lattice QCD calculations of the B {yields} D and B {yields} D* form factors and discuss prospects for their improvement. Successful calculations within the quenched approximation demonstrate the power of lattice methods for calculating F(1) and G(1), and the unquenched calculations in progress should soon allow for a 2-3% exclusive determination of |Vcb|.

Authors:
;
Publication Date:
Research Org.:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
917832
Report Number(s):
FERMILAB-CONF-07-057-T
TRN: US0805140
DOE Contract Number:
AC02-07CH11359
Resource Type:
Conference
Resource Relation:
Conference: Presented at 4th International Workshop on the CKM Unitarity Triangle (CKM 2006), Nagoya, Japan, 12-16 Dec 2006
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; APPROXIMATIONS; FORM FACTORS; QUANTUM CHROMODYNAMICS; UNITARITY; Lattice

Citation Formats

Van de Water, R.S., and /Fermilab. Lattice QCD results for the B --> D(*) l nu form factors: F(1) and G(1). United States: N. p., 2007. Web.
Van de Water, R.S., & /Fermilab. Lattice QCD results for the B --> D(*) l nu form factors: F(1) and G(1). United States.
Van de Water, R.S., and /Fermilab. Mon . "Lattice QCD results for the B --> D(*) l nu form factors: F(1) and G(1)". United States. doi:. https://www.osti.gov/servlets/purl/917832.
@article{osti_917832,
title = {Lattice QCD results for the B --> D(*) l nu form factors: F(1) and G(1)},
author = {Van de Water, R.S. and /Fermilab},
abstractNote = {I review the current status of lattice QCD calculations of the B {yields} D and B {yields} D* form factors and discuss prospects for their improvement. Successful calculations within the quenched approximation demonstrate the power of lattice methods for calculating F(1) and G(1), and the unquenched calculations in progress should soon allow for a 2-3% exclusive determination of |Vcb|.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

Conference:
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  • The exclusive semileptonic decays B{r_arrow}D{sub 1}(2420)l{bar {nu}} and B{r_arrow}D{sub 2}{sup *}(2460)l{bar {nu}} are studied at the subleading order of heavy quark expansion. The subleading Isgur-Wise functions resulting from the kinetic energy and chromomagnetic corrections to the HQET Lagrangian are calculated by QCD sum rules in the framework of heavy quark effective theory. The decay rates and branching ratios are computed with the inclusion of the order of 1/m{sub Q} corrections. It is found that the 1/m{sub Q} correction to the decay rate is not large for B{r_arrow}D{sub 2}{sup *} but is very large for B{r_arrow}D{sub 1}.
  • We report on a lattice-QCD calculation of the B to pi l nu form factor with domain-wall light quarks and relativistic b-quarks using the 2 + 1 flavor domain-wall fermion and Iwasaki gauge-field ensembles generated by the RBC and UKQCD Collaborations. We present initial results obtained from the coarser (a ~ 0.11 fm) 24^3 lattices and some of the finer (a ~ 0.086 fm) 32^3 lattices.
  • We calculate the form factors for B → πℓν and B s → Kℓν decay in dynamical lattice quantum chromodynamics (QCD) using domain-wall light quarks and relativistic b-quarks. We use the (2+1)-flavor gauge-field ensembles generated by the RBC and UKQCD collaborations with the domain-wall fermion action and Iwasaki gauge action. For the b-quarks we use the anisotropic clover action with a relativistic heavy-quark interpretation. We analyze data at two lattice spacings of a ≈ 0.11, 0.086 fm with unitary pion masses as light as M π ≈ 290 MeV. We simultaneously extrapolate our numerical results to the physical light-quark massesmore » and to the continuum and interpolate in the pion/kaon energy using SU(2) “hard-pion” chiral perturbation theory for heavy-light meson form factors. We provide complete systematic error budgets for the vector and scalar form factors f + (q 2) and f 0(q 2) for both B → πℓν and B s → Kℓν at three momenta that span the q 2 range accessible in our numerical simulations. Next we extrapolate these results to q 2 = 0 using a model-independent z-parametrization based on analyticity and unitarity. We present our final results for f +(q 2) and f 0(q 2)as the coefficients of the series in z and the matrix of correlations between them; this provides a parametrization of the form factors valid over the entire allowed kinematic range. Our results agree with other three-flavor lattice-QCD determinations using staggered light quarks, and have comparable precision, thereby providing important independent cross-checks. Both B → πℓν and B s → Kℓν decays enable determinations of the Cabibbo-Kobayashi-Maskawa matrix element |V ub|. Furthermore, we perform a combined z-fit of our numerical B → πℓν form-factor data with the experimental measurements of the branching fraction from BABAR and Belle leaving the relative normalization as a free parameter; we obtain |V ub| = 3.61(32)×10 -3, where the error includes statistical and all systematic uncertainties. The same approach can be applied to the decay B s → Kℓν to provide an alternative determination of |V ub| once the process has been measured experimentally. In anticipation of future experimental measurements, we make predictions for B → πℓν and B s → Kℓν differential branching fractions and forward-backward asymmetries in the Standard Model.« less
  • We compute themore » $$B\to\pi\ell\nu$$ semileptonic form factors and update the determination of the CKM matrix element $$|V_{ub}|$$. We use the MILC asqtad ensembles with $$N_f=2+1$$ sea quarks at four different lattice spacings in the range $$a \approx 0.045$$~fm to $0.12$~fm. The lattice form factors are extrapolated to the continuum limit using SU(2) staggered chiral perturbation theory in the hard pion limit, followed by an extrapolation in $q^2$ to the full kinematic range using a functional $z$-parameterization. The extrapolation is combined with the experimental measurements of the partial branching fraction to extract $$|V_{ub}|$$. Our preliminary result is $$|V_{ub}|=(3.72\pm 0.14)\times 10^{-3}$$, where the error reflects both the lattice and experimental uncertainties, which are now on par with each other.« less