Determination of $|V_{ub}|$ from Measurements of the Electron and Neutrino Momenta in Inclusive Semileptonic $B$ Decays

We present a determination of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{ub}|$ based on the analysis of semileptonic $B$ decays from a sample of $88\times {10}^6$ ${\rm Y}(4S)$ decays collected with the BABAR detector at the SLAC PEP-II $e^{+}{e}^{-}$ storage ring. Charmless semileptonic $B$ decays are selected using measurements of the electron energy and the invariant mass squared of the electron-neutrino pair. We obtain $|V_{ub}|=(3.95\pm {0.26}_{-0.42}^{+0.58}\pm 0.25)\times {10}^{-3}$, where the errors represent experimental uncertainties, heavy quark parameter uncertainties, and theoretical uncertainties, respectively.

Figure 1

The difference between the two neutrino energy estimates described in the text for continuum-subtracted data and simulated $B\overline{B}$ events for the $De\overline{\nu }$ control sample.

Figure 2

The electron energy, $E_e$, and $s_h^{\max }$ spectra in the ${\rm Y}(4S)$ frame for continuum-subtracted data and simulated $B\overline{B}$ events satisfying all selection requirements except for the variable shown. The arrows denote the signal (and sideband) region in $E_e$ and $s_h^{\max }$. Note that ${\tilde{E}}_e\ne E_e$ (see text).