Semileptonic B Decays with Nf=2+1 Dynamical Quarks

Semileptonic, B --> pi l,nu, decays are studied on the MILC dynamical configurations using NRQCD heavy and Asqtad light quarks. We work with light valence quark masses ranging between m_s and m_s/8. Preliminary simple linear chiral extrapolations have been carried out for form factors f_para and f_perp at fixed E_pi. The chirally extrapolated results for the form factors f_+(q^2) and f_0(q^2) are then fit to the Becirevic-Kaidalov (BK) ansatz. Preliminary estimates of the CKM matrix element |V_{ub}| are presented based on the recently published branching fractions for B exclusive semileptonic decays by the CLEO collaboration.