Lattice QCD form factor for Bs→D∗slν at zero recoil with nonperturbative current renormalization

We present details of a lattice QCD calculation of the B s → D ∗ s axial form factor at zero recoil using the highly improved staggered quark (HISQ) formalism on the second-generation MILC gluon ensembles that include up, down, strange and charm quarks in the sea. Using the HISQ action for all valence quarks means that the lattice axial vector current that couples to the W can be renormalized fully nonperturbatively, giving a result free of the perturbative matching errors that previous lattice QCD calculations have had. We calculate correlation functions at three values of the lattice spacing, and multiple b -quark masses, for physical c and s . The functional dependence on the b -quark mass can be determined and compared to heavy quark effective theory expectations, and a result for the form factor obtained at the physical value of the b -quark mass. We find F B s → D ∗ s ( 1 ) = h s A 1 ( 1 ) = 0.9020 ( 96 ) stat ( 90 ) sys . This is in agreement with earlier lattice QCD results, which use NRQCD b quarks, with a total uncertainty reduced by more than a factor of 2. We discuss implications of this result for the B → D ∗ axial form factor at zero recoil and for determinations of V c b

Renormalising vector currents in lattice QCD using momentum-subtraction schemes

No abstract available

Bottomonium precision tests from full lattice QCD: Hyperfine splitting, Υ leptonic width, and b quark contribution to e+e− → hadrons

We calculate the mass difference between the Υ and η b and the Υ leptonic width from lattice QCD using the Highly Improved Staggered Quark formalism for the b quark and including u , d , s and c quarks in the sea. We have results for lattices with lattice spacing as low as 0.03 fm and multiple heavy quark masses, enabling us to map out the heavy quark mass dependence and determine values at the b quark mass. Our results are: M Υ − M η b = 57.5 ( 2.3 ) ( 1.0 ) M e V (where the second uncertainty comes from neglect of quark-line disconnected correlation functions) and decay constants, f η b = 724 ( 12 ) MeV and f Υ = 677.2 ( 9.7 ) MeV, giving Γ ( Υ → e + e − ) = 1.292 ( 37 ) ( 3 ) k e V . The hyperfine splitting and leptonic width are both in good agreement with experiment, and provide the most accurate lattice QCD results to date for these quantities by some margin. At the same time results for the time moments of the vector-vector correlation function can be compared to values for the b quark contribution to σ ( e + e − → h a d r o n s ) determined from experiment. Moments 4–10 provide a 2% test of QCD and yield a b quark contribution to the anomalous magnetic moment of the muon of 0.300(15) × 10 − 10 . Our results, covering a range of heavy quark masses, may also be useful to constrain QCD-like composite theories for beyond the Standard Model physics

Determination of m¯b / m¯c and m¯b from nf = 4 lattice QCD + QED

We extend HPQCD’s earlier n f = 2 + 1 + 1 lattice-QCD analysis of the ratio of ¯¯¯¯¯¯ MS masses of the b and c quark to include results from finer lattices (down to 0.03 fm) and a new calculation of QED contributions to the mass ratio. We find that ¯ m b ( μ ) / ¯ m c ( μ ) = 4.586 ( 12 ) at renormalization scale μ = 3     GeV . This result is nonperturbative. Combining it with HPQCD’s recent lattice QCD + QED determination of ¯ m c ( 3     GeV ) gives a new value for the b -quark mass: ¯ m b ( 3     GeV ) = 4.513 ( 26 )     GeV . The b -mass corresponds to ¯ m b ( ¯ m b , n f = 5 ) = 4.202 ( 21 )     GeV . These results are the first based on simulations that include QED