  We update the lattice calculation of the $B\to\pi$ semileptonic form factors,
which have important applications to the CKM matrix element $|V_{ub}|$ and the
$B\to\pi\ell^+\ell^-$ rare decay. We use MILC asqtad ensembles with $N_f=2+1$
sea quarks and over a range of lattice spacings $a \approx 0.045$--$0.12$ fm.
We perform a combined chiral and continuum extrapolation of our lattice data
using SU(2) staggered chiral perturbation theory in the hard pion limit. To
extend the results for the form factors to the full kinematic range, we take a
functional approach to parameterize the form factors using the
Bourrely-Caprini-Lellouch formalism in a model-independent way. Our analysis is
still blinded with an unknown off-set factor which will be disclosed when we
present the final results.
