B→Dℓν form factors at nonzero recoil and |Vcb| from 2+1-flavor lattice QCD
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Lattice, F., Collaborations, M. I. L. C., Bailey, J. A., Bazavov, A., Bernard, C., Bouchard, C. M., ... & Freeland, E. D. (2015). B→ D ℓ ν form factors at nonzero recoil and| V c b| from 2+ 1-flavor lattice QCD. Physical Review D, 92(3), 034506. [https://doi.org/10.1103/PhysRevD.92.034506]
SponsorshipNational Science Foundation's Teragrid/XSEDE Program; United States Department of Energy (DOE) DE-FG02-91ER40628 DE-FC02-06ER41446 DE-SC0010120 DE-FG02-91ER40661 DE-FG02-13ER42001 DE-FG02-ER41976; National Science Foundation (NSF) PHY10-67881 PHY10-034278 PHY14-17805 PHY09-03571 PHY13-16748; URA Visiting Scholars' program; Spanish Government FPA2010-16696; Junta de Andalucia FQM-101 FQM-6552; European Commission Joint Research Centre PCIG10-GA-2011-303781; German Excellence Initiative; European Union (EU) 291763; European Union (EU); National Research Foundation of Korea (NRF) - Ministry of Education 2014027937; NRF grant - Korean government (MEST) 2014001852; United States Department of Energy (DOE) DE-AC02-98CH10886; Fermi Research Alliance, LLC DE-AC02-07CH11359
We present the first unquenched lattice-QCD calculation of the hadronic form factors for the exclusive decay ¯B→Dℓ¯ν at nonzero recoil. We carry out numerical simulations on 14 ensembles of gauge-field configurations generated with 2+1 flavors of asqtad-improved staggered sea quarks. The ensembles encompass a wide range of lattice spacings (approximately 0.045 to 0.12 fm) and ratios of light (up and down) to strange sea-quark masses ranging from 0.05 to 0.4. For the b and c valence quarks we use improved Wilson fermions with the Fermilab interpretation, while for the light valence quarks we use asqtad-improved staggered fermions. We extrapolate our results to the physical point using rooted staggered heavy-light meson chiral perturbation theory. We then parametrize the form factors and extend them to the full kinematic range using model-independent functions based on analyticity and unitarity. We present our final results for f+(q2) and f0(q2), including statistical and systematic errors, as coefficients of a series in the variable z and the covariance matrix between these coefficients. We then fit the lattice form-factor data jointly with the experimentally measured differential decay rate from BABAR to determine the CKM matrix element, |Vcb|=(39.6±1.7QCD+exp±0.2QED)×10−3. As a byproduct of the joint fit we obtain the form factors with improved precision at large recoil. Finally, we use them to update our calculation of the ratio R(D) in the Standard Model, which yields R(D)=0.299(11).