Measurements of B→{π,η,η^{′}}lν_{l} Branching Fractions and Determination of |V_{ub}| with Semileptonically Tagged B Mesons

We report measurements of branching fractions for the decays B -> Pl nu(l), where P are the pseudoscalar charmless mesons pi(-), pi(0), eta and eta('), based on 348 fb(-1) of data collected with the BABAR detector, using B-0 and B+ mesons found in the recoil of a second B meson decaying as B -> D-(*())l nu(l). Assuming isospin symmetry, we combine pionic branching fractions to obtain B(B-0 -> pi(-)l(+)nu(l)) = (1.54 +/- 0.17((stat)) +/- 0.09((syst))) x 10(-4); we find 3.2 sigma evidence of the decay B+ -> eta l(+)nu(l) and measure its branching fraction to be (0.64 +/- 0.20((stat))+/- 0.03((syst)))x10(-4), and determine B(B+ -> eta'l(+)nu(l)) <0.47 x 10(-4) to 90% confidence level. Using partial branching fractions for the pionic decays in ranges of the momentum transfer and a variety of form factor calculation, we obtain values of the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-ub vertical bar in ranging from 3.6 x 10(-3) to 4.1 x 10(-3).