Lattice QCD calculation of the B-(s) -> D-(s)* lv form factors at zero recoil and implications for vertical bar V-cb vertical bar

© 2018 authors. We present results of a lattice QCD calculation of B→D∗ and Bs→Ds∗ axial vector matrix elements with both states at rest. These zero recoil matrix elements provide the normalization necessary to infer a value for the CKM matrix element |Vcb| from experimental measurements of B0→D∗+ -ν and Bs0→Ds∗+ -ν decay. Results are derived from correlation functions computed with highly improved staggered quarks (HISQ) for light, strange, and charm quark propagators, and nonrelativistic QCD for the bottom quark propagator. The calculation of correlation functions employs MILC Collaboration ensembles over a range of three lattice spacings. These gauge field configurations include sea quark effects of charm, strange, and equal-mass up and down quarks. We use ensembles with physically light up and down quarks, as well as heavier values. Our main results are FB→D∗(1)=0.895±0.010stat±0.024sys and FBs→Ds∗(1)=0.883±0.012stat±0.028sys. We discuss the consequences for |Vcb| in light of recent investigations into the extrapolation of experimental data to zero recoil.This work was funded in part by STFC grants ST/L000385/1 and ST/L000466/1. The results described here were obtained using the Darwin Supercomputer of the University of Cambridge High Performance Computing Service as part of the DiRAC facility jointly funded by STFC, the Large Facilities Capital Fund of BIS and the Universities of Cambridge and Glasgow. This equipment was funded by BIS National E-infrastructure capital grant (ST/K001590/1), STFC capital grants ST/H008861/1 and ST/H00887X/1, and STFC DiRAC Operations grants ST/K00333X/1, ST/M007073/1, and ST/P002315/1. MW is grateful for an IPPP Associateship held while this work was undertaken