skip to main content


Title: $$|V_{ub}|$$ from $$B\to\pi\ell\nu$$ decays and (2+1)-flavor lattice QCD

We present a lattice-QCD calculation of the B → πℓν semileptonic form factors and a new determination of the CKM matrix element |V ub|. We use the MILC asqtad (2+1)-flavor lattice configurations at four lattice spacings and light-quark masses down to 1/20 of the physical strange-quark mass. We extrapolate the lattice form factors to the continuum using staggered chiral perturbation theory in the hard-pion and SU(2) limits. We employ a model-independent z parametrization to extrapolate our lattice form factors from large-recoil momentum to the full kinematic range. We introduce a new functional method to propagate information from the chiral-continuum extrapolation to the z expansion. We present our results together with a complete systematic error budget, including a covariance matrix to enable the combination of our form factors with other lattice-QCD and experimental results. To obtain |V ub|, we simultaneously fit the experimental data for the B → πℓν differential decay rate obtained by the BABAR and Belle collaborations together with our lattice form-factor results. We find |V ub|=(3.72±0.16) × 10 –3, where the error is from the combined fit to lattice plus experiments and includes all sources of uncertainty. Our form-factor results bring the QCD error on |V ub| tomore » the same level as the experimental error. We also provide results for the B → πℓν vector and scalar form factors obtained from the combined lattice and experiment fit, which are more precisely determined than from our lattice-QCD calculation alone. Lastly, these results can be used in other phenomenological applications and to test other approaches to QCD.« less
 [1] ;
  1. Seoul National Univ., Seoul (South Korea). et al.
Publication Date:
Report Number(s):
Journal ID: ISSN 1550-7998; PRVDAQ; arXiv eprint number arXiv:1503.07839; TRN: US1600932
Grant/Contract Number:
AC02-07CH11359; FG02-91ER40628; FC02-12ER41879; SC0010120; FG02-91ER40661; FC02-06ER41443; FG02-13ER42001; No. DE-FG02-13ER41976; SC0010114
Accepted Manuscript
Journal Name:
Physical Review. D, Particles, Fields, Gravitation and Cosmology
Additional Journal Information:
Journal Volume: 92; Journal Issue: 1; 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:
Fermilab Lattice and MIC Collaborations
Country of Publication:
United States
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1213805