Measurements of Partial Branching Fractions for ¯¯¯B→Xul¯ν and Determination of |Vub|

Abstract

We present partial branching fractions for inclusive charmless semileptonic B decays ¯¯¯ B → X u ℓ ¯ ν , and the determination of the Cabibbo-Kobayashi-Maskawa matrix element | V u b | . The analysis is based on a sample of 383 × 10 6 Υ ( 4 S ) decays into B ¯¯¯ B pairs collected with the BABAR detector at the SLAC PEP-II e + e − storage rings. We select events using the invariant mass M X of the hadronic system, the invariant mass squared, q 2 , of the lepton and neutrino pair, the kinematic variable P + , or one of their combinations. We then determine partial branching fractions in limited regions of phase space: Δ B = ( 1.18 ± 0.09 stat ± 0.07 syst ± 0.01 theor ) × 10 − 3 ( M X < 1.55 GeV / c 2 ), Δ B = ( 0.95 ± 0.10 stat ± 0.08 syst ± 0.01 theor ) × 10 − 3 ( P + < 0.66 GeV / c ), and Δ B = ( 0.81 ± 0.08 stat ± 0.07 syst ± 0.02 theor ) × 10 − 3 ( M X < 1.7 GeV / c 2 , q 2 > 8 GeV 2 / c 4 ). Corresponding values of | V u b | are extracted using several theoretical calculations.