We present results of a lattice QCD calculation of B → D Ã and B s → D Ã s 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 jV cb j from experimental measurements ofBResults 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 F B→D Ã ð1Þ ¼ 0.895 AE 0.010 stat AE 0.024 sys and F B s →D Ã s ð1Þ ¼ 0.883 AE 0.012 stat AE 0.028 sys . We discuss the consequences for jV cb j in light of recent investigations into the extrapolation of experimental data to zero recoil.

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We use our lattice QCD computation of the Bc → J/ψ form factors to determine the differential decay rate for the semitauonic decay channel and construct the ratio of branching fractions R(J/ψ) = B(B − c → J/ψτ − ντ )/B(B − c → J/ψµ − νµ). We find R(J/ψ) = 0.2601(36) and give an error budget. We also extend the relevant angular observables, which were recently suggested for the study of lepton flavor universality violating effects in B → D * ν, to Bc → J/ψ ν and make predictions for their values under different new physics scenarios.

We present the status of our ongoing calculation of the zero-recoil form factor for the semileptonic decayB 0 → D * + l −ν using lattice QCD with 2+1+1 flavours of highly improved staggered quarks in the sea (the MILC HISQ configurations) and using non-relativistic QCD for the bottom quark. We combine our result for F(1) with the latest HFAG average of η EW F(1)|V cb | to get a preliminary value for |V cb |.

Predicting the B 0 s −B 0 s width difference ∆Γs relies on the heavy quark expansion and on hadronic matrix elements of ∆B = 2 operators. We present the first lattice QCD results for matrix elements of the dimension-7 operators R2,3 and linear combinationsR2,3 using nonrelativistic QCD for the bottom quark and a highly improved staggered quark (HISQ) action for the strange quark. Computations use MILC ensembles of gauge field configuations with 2 + 1 + 1 flavors of sea quarks with the HISQ discretization, including lattices with physically light up/down quark masses. We discuss features unique to calculating matrix elements of these operators and analyze uncertainties from series truncation, discretization, and quark mass dependence. Finally we report the first Standard Model determination of ∆Γs using lattice QCD results for all hadronic matrix elements through O(1/m b ). The main result of our calculations yields the 1/m b contribution ∆Γ 1/m b = −0.022(10) ps −1 . Adding this to the leading order contribution, the Standard Model prediction is ∆Γs = 0.092(14) ps −1 .Oscillations of neutral mesons into their antiparticles have been important phenomena in the study of quark flavor. This flavor-changing, neutral mixing is absent in the Standard Model (SM) at the classical level; appearing at one-loop level it is suppressed by two powers of Fermi's constant G F relative to hadronic and quark mass scales. A few observables are, to a high level of precision, sensitive only to short-distance physics. Within the Standard Model, predictions for these are reliably calculable because the dominant contribution comes from top-quark loops; there is no significant contribution from intermediate-state hadronic physics. Prime examples are: in the mixing of strange mesons K 0 −K 0 , the indirect CP-violating ratio ϵ K and, in beauty mesons B 0 d,s −B 0 d,s , the mass differences (equivalently, the oscillation frequencies) ∆M d,s . Precise experimental measurements of these, together with accurate Standard Model predictions, constitute stringent tests of the SM description of quark flavor.Beyond these observables are others, where contributions from hadronic intermediate states must be included. For example, mixing in neutral charm mesons D 0 −D 0 has significant long-distance contributions due to differing flavor structure from K 0 and B 0 mixing. Predictions for heavy meson and baryon lifetimes also require theoretical treatment of long-distance effects.The B 0 s −B 0 s width difference ∆Γ s is another example and is the focus of this paper. Unlike the mass difference, which comes from the real part of the mixing a M.Wingate@damtp.cam.ac.uk b http://www.physics.gla.ac.uk/HPQCD amplitude, the width difference comes from the imaginary part which, by the optical theorem, describes the decays to real final states, primarily b → ccs decays. Consequently, ∆Γ s is dominantly due to processes with intrinsic charm and we expect it to be insensitive to new physics. Comparison between theory and experiment is a test of the theoretical met...