Determination of |Vub| using the lepton energy spectrum in events tagged with a fully reconstructed B meson

Abstract

We present measurements of partial branching fractions for the inclusive semileptonic decay of B ! Xu` (` = e or ) leading to the determination of the CKM matrix element jVubj. This analysis is based on a sample of 460 million BB events recorded at the (4S) resonance at the BABAR detector. We select B ! Xu` events using the energy spectrum of the lepton (E`) in an event where one of the B-mesons is fully reconstructed. We measure partial branching fractions in restricted regions of the E` spectrum, which are translated into values of jVubj using four theoretical approaches. We calculate the arithmetic mean, using the results from the four theoretical approaches at E` > 1:5 GeV resulting in: jVubj = (4:68+0:31 ð€€€0:32) 10ð€€€3. The analysis presented in this thesis is the rst time a measurement of jVubj has been performed using the E` spectrum in events tagged with a fully reconstructed B meson.