B meson semileptonic form factors from unquenched lattice QCD

The semileptonic process, $B\ensuremath{\rightarrow}\ensuremath{\pi}l\ensuremath{\nu}$, is studied via full QCD lattice simulations. We use unquenched gauge configurations generated by the MILC Collaboration. These include the effect of vacuum polarization from three quark flavors: the $s$ quark and two very light flavors ($u/d$) of variable mass allowing extrapolations to the physical chiral limit. We employ nonrelativistic QCD to simulate the $b$ quark and a highly improved staggered quark action for the light sea and valence quarks. We calculate the form factors ${f}_{+}({q}^{2})$ and ${f}_{0}({q}^{2})$ in the chiral limit for the range $16\text{ }\text{ }{\mathrm{GeV}}^{2}\ensuremath{\le}{q}^{2}l{q}_{\mathrm{max} }^{2}$ and obtain ${\ensuremath{\int}}_{16\text{ }\text{ }{\mathrm{GeV}}^{2}}^{{q}_{\mathrm{max} }^{2}}[d\ensuremath{\Gamma}/d{q}^{2}]d{q}^{2}/|{V}_{ub}{|}^{2}=1.46(35)\text{ }\text{ }{\mathrm{ps}}^{\ensuremath{-}1}$. Combining this with a preliminary average by the Heavy Flavor Averaging Group (HFAG'05) of recent branching fraction data for exclusive $B$ semileptonic decays from the BABAR, Belle and CLEO Collaborations leads to $|{V}_{ub}|=4.22(30)(51)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$.