Measurement of the B(0) -> pi(-)l(+)nu and B(+) -> eta(l)l(+)nu branching fractions the B(0) -> pi(-)l(+)nu and B(+) -> eta l(+)nu form- factor shapes and determination of vertical bar V(ub)vertical bar

We report the results of a study of the exclusive charmless semileptonic decays B(+) -> eta(l)l(+)nu and B(0) -> pi(-)l(+)nu undertaken with approximately 464 x 10(6) B (B) over bar pairs collected at the Y(4S) resonance with the BABAR detector. The analysis uses events in which the signal B decays are reconstructed with a loose neutrino reconstruction technique. We obtain partial branching fractions for B(+) -> eta l(+)nu and B(0) -> pi(-)l(+)nu decays in three and 12 bins of q(2) respectively from which we extract the f (+)(q(2)) form-factor shapes and the total branching fractions B(B(+) -> eta l(+)nu)= (0.36 +/- 0.05(stat) +/- 0.04(syst)) x 10(-4) and B(B(0) -> pi(-)l(+)nu) = (1.42 +/- 0.05(stat) +/- 0.07(syst)) x 10(-4). We also measure B(B(+) -> eta'l(+)nu) = (0.24 +/- 0.08(stat) +/- 0.03(syst)) x 10(-4). We obtain values for the magnitude of the CKM matrix element |V(ub)| using three different QCD calculations.