Measurement of the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-ub vertical bar with B -> pe nu decays

We present a measurement of the branching fraction for the rare decays B-->rhoenu and extract a value for the magnitude of V-ub, one of the smallest elements of the Cabibbo-Kobayashi-Maskawa quark-mixing matrix. The results are given for five different calculations of form factors used to parametrize the hadronic current in semileptonic decays. Using a sample of 55x10(6) B (B) over bar meson pairs recorded with the BABAR detector at the PEP-II e(+)e(-) storage ring, we obtain B(B-0-->rho(-)e(+)nu)=(3.29+/-0.42+/-0.47+/-0.55)x10(-4) and V-ub=(3.64+/-0.22+/-0.25(-0.56)(+0.39))x10(-3), where the uncertainties are statistical, systematic, and theoretical, respectively.