Rare decay B -> K ll form factors from lattice QCD

We calculate, for the first time using unquenched lattice QCD, form factors for the rare decay B -> Kll in and beyond the Standard Model. Our lattice QCD calculation utilizes a nonrelativistic QCD formulation for the b valence quarks, the highly improved staggered quark formulation for the light valence quarks, and employs the MILC 2+1 asqtad ensembles. The form factor results, based on the z expansion, are valid over the full kinematic range of q^2. We construct the ratios f0/f+ and fT/f+, which are useful in constraining new physics and verifying effective theory form factor symmetry relations. We also discuss the calculation of Standard Model observables.

Standard Model predictions for B -> Kll with form factors from lattice QCD

We calculate, for the first time using unquenched lattice QCD form factors, the Standard Model differential branching fractions $dB/dq^2(B to Kll)$ for $l=e, mu, tau$ and compare with experimental measurements by Belle, BABAR, CDF, and LHCb. We report on $mathcal{B}(B to Kll)$ in $q^2$ bins used by experiment and predict $mathcal{B}(B to K tau tau) = (1.44 pm 0.15) 10^{-7}$. We also calculate the ratio of branching fractions $R^mu_e = 1.00023(63)$ and predict $R^tau_l = 1.159(40)$, for $l=e, mu$. Finally, we calculate the flat term in the angular distribution of the differential decay rate $F_H^{e, mu, tau}$ in experimentally motivated $q^2$ bins.