Determination of the CKM element V(ub)

The precise determination of the CKM matrix element |V_ub | is crucial in testing the Standard Model mechanism for CP violation. From a sample of 88 million BB¯ pairs collected with the BABAR detector, charmless semileptonic B decays are selected using simultaneous requirements on the electron energy, E_e, and the invariant mass squared of the electron-neutrino pair, q². The partial branching fraction, unfolded for detector effects, is determined in a region of the q²-E_e plane where the dominating semileptonic decays to charm mesons are highly suppressed. Theoretical calculations based on the Heavy Quark Expansion allows for a determination of |V_ub| = (3.95 ± 0.27[special characters omitted] ± 0.25) × 10^-3, where the errors represent experimental, heavy quark parameters and theoretical uncertainties, respectively.