Measurement of the decay $B^0topi^-ell^+ u$ and determination of $|V_{ub}|$

We present a measurement of the charmless semileptonic decay $B^0topi^-ell^+ u$ using a data sample containing 657$times 10^6$ $Bbar{B}$ events collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider operating near the $Upsilon(4S)$ resonance. We determine the total branching fraction of the decay, $mathcal{B}(B^0topi^-ell^+ u)=(1.49pm 0.04{(mathrm{stat})}pm 0.07{(mathrm{syst})})times 10^{-4}$. We also report a new precise measurement of the differential decay rate, and extract the Cabibbo-Kobayashi-Maskawa matrix element $|V_{ub}|$ using model-independent and -dependent approaches. From a simultaneous fit to the measured differential decay rate and lattice QCD results, we obtain $|V_{ub}|=(3.43pm 0.33)times 10^{-3}$, where the error includes both statistical and systematic uncertainties.