$B\to\pi\ell\nu$ semileptonic form factors from unquenched lattice QCD   and determination of $|V_{ub}|$
  We compute the $B\to\pi\ell\nu$ semileptonic form factors and update the determination of the CKM matrix element $|V_{ub}|$. We use the MILC asqtad ensembles with $N_f=2+1$ sea quarks at four different lattice spacings in the range $a \approx 0.045$~fm to $0.12$~fm. The lattice form factors are extrapolated to the continuum limit using SU(2) staggered chiral perturbation theory in the hard pion limit, followed by an extrapolation in $q^2$ to the full kinematic range using a functional $z$-parameterization. The extrapolation is combined with the experimental measurements of the partial branching fraction to extract $|V_{ub}|$. Our preliminary result is $|V_{ub}|=(3.72\pm 0.14)\times 10^{-3}$, where the error reflects both the lattice and experimental uncertainties, which are now on par with each other. 
J. A. Bailey, A. Bazavov, C. Bernard, C. Bouchard, C. DeTar, D. Du, A.   X. El-Khadra, J. Foley, E. D. Freeland, E. Gamiz, S...
hep-lat