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Title: $$B \to \pi \ell \nu$$ and $$B_s \to K \ell \nu$$ form factors and $$|V_{ub}|$$ from 2+1-flavor lattice QCD with domain-wall light quarks and relativistic heavy quarks

We calculate the form factors for B → πℓν and Bs → 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 Mπ ≈ 290 MeV. We simultaneously extrapolate our numerical results to the physical light-quark masses 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 + (q2) and f0(q2) for both B → πℓν and Bs → Kℓν at three momenta that span the q2 range accessible in our numerical simulations. Next we extrapolate these results to q2 = 0 using a model-independent z-parametrization based on analyticity and unitarity. We present our final results for f+(q2) and f0(q2)as the coefficients of the series in z and the matrix of correlations between them;more » 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 Bs → Kℓν decays enable determinations of the Cabibbo-Kobayashi-Maskawa matrix element |Vub|. 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 |Vub| = 3.61(32)×10-3, where the error includes statistical and all systematic uncertainties. The same approach can be applied to the decay Bs → Kℓν to provide an alternative determination of |Vub| once the process has been measured experimentally. In anticipation of future experimental measurements, we make predictions for B → πℓν and Bs → Kℓν differential branching fractions and forward-backward asymmetries in the Standard Model.« less
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  1. Univ. of Southampton, Southampton (United Kingdom)
  2. Brookhaven National Lab. (BNL), Upton, NY (United States)
  3. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
  4. Boston Univ., Boston, MA (United States)
Publication Date:
OSTI Identifier:
Report Number(s):
Journal ID: ISSN 1550-7998; arXiv eprint number arXiv:1501.05373; TRN: US1600873
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Physical Review. D, Particles, Fields, Gravitation and Cosmology
Additional Journal Information:
Journal Volume: 91; Journal Issue: 7; Journal ID: ISSN 1550-7998
American Physical Society (APS)
Research Org:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
Contributing Orgs:
RBC Collaboration; UKQCD Collaboration
Country of Publication:
United States