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Charmless semileptonic decays, B -> X_u l nu, are studied in a
sample of 232 million B Bbar decays recorded with the BaBar detector,
in events where the decay of the second B meson is fully
reconstructed. Inclusive charmless decays are selected in kinematic
regions where the dominant background from semileptonic B decays to
charm is reduced by requirements on the hadronic mass M_X and the
momentum transfer q^2. The partial branching fraction for B -> X_u
l nu decays for M_X < 1.7 GeV/c^2 and q^2 > 8 GeV^2/c^4 is measured to
be DeltaB(B -> X_u l nu) = (0.87 +/- 0.09 (stat) +/- 0.09 (sys) +/-
0.01 (th))x 10^-3. The CKM matrix element |V_{ub}| is determined by
using theoretical calculations of phase space acceptances. Theoretical
uncertainties in this extrapolation are reduced by using the inclusive
b -> s gamma photon spectrum and moments of the b -> c l nu lepton
energy and hadronic invariant mass.
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