B meson semileptonic form factors from unquenched lattice QCD -: art. no. 074502

The semileptonic process, B ->pi l 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 GeV2<= q(2)< q(max)(2) and obtain integral(16GeV2)(qmax2)[d Gamma/dq(2)]dq(2)/\V-ub\(2)=1.46(35) ps(-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)x10(-3).