Measurement of the Cabibbo-Kobayashi-Maskawa Matrix Element|Vub|withB→ρeνDecays

We present a measurement of the branching fraction for the rare decays $B\to \rho e\nu$ 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 $55\times {10}^6$ $B\overline{B}$ meson pairs recorded with the BABAR detector at the PEP-II $e^{+}{e}^{-}$ storage ring, we obtain $\mathcal{B}(B^0\to {\rho }^{-}{e}^{+}\nu )=(3.29\pm 0.42\pm 0.47\pm 0.55)\times {10}^{-4}$ and $|V_{ub}|=(3.64\pm 0.22\pm {0.25}_{-0.56}^{+0.39})\times {10}^{-3}$, where the uncertainties are statistical, systematic, and theoretical, respectively.