R(J/ψ) and B_{c}

We use our lattice QCD computation of the B_{c}→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^{-}ν[over ¯]_{τ})/B(B_{c}^{-}→J/ψµ^{-}ν[over ¯]_{µ}). We find R(J/ψ)=0.2582(38) 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^{*}ℓν, to B_{c}→J/ψℓν and make predictions for their values under different new physics scenarios.

Lattice QCD Matrix Elements for the B_{s}

Predicting the B_{s}^{0}-B[over ¯]_{s}^{0} width difference ΔΓ_{s} relies on the heavy quark expansion and on hadronic matrix elements of ΔB=2 operators. We present the first lattice QCD results for matrix elements of the dimension-7 operators R_{2,3} and linear combinations R[over ˜]_{2,3} using nonrelativistic QCD for the bottom quark and a highly improved staggered quark (HISQ) action for the strange quark. Computations use MILC Collaboration ensembles of gauge field configurations with 2+1+1 flavors of sea quarks with the HISQ discretization, including lattices with physically light up or 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 ΔΓ_{s} 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 ΔΓ_{1/m_{b}}=-0.022(10) ps^{-1}. Adding this to the leading order contribution, the standard model prediction is ΔΓ_{s}=0.092(14) ps^{-1}.