A consistent treatment of B → πlν decay is given on the light-front. The B to π transition form factors are calculated in the entire physical range of momentum transfer for the first time. The valence-quark contribution is obtained using relativistic light-front wave functions. Higher quark-antiquark Fock-state of the B-meson bound state is represented effectively by the |B*π〉 configuration, and its effect is calculated in the chiral perturbation theory. Wave function renormalization is taken into account consistently. The |B*π〉) contribution dominates near the zero-recoil point (q2 ≃ 25 GeV2), and decreases rapidly as the recoil momentum increases. The calculated form factor f+(q2) follows approximately a dipole q2-dependence in the entire range of momentum transfer. We estimate that |Vub|=0.003.
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