Determination of |Vub| from Measurements of the Inclusive Charmless Semileptonic Partial Rates of B Mesons using Full Reconstruction Tags

We present a measurement of the Cabibbo-Kobayashi-Maskawa matrix element data collected by the Belle detector at the KEKB e+e-asymmetric collider. Events are tagged by fully reconstructing one of the B mesons, produced in pairs from Υ(4S). The signal for b→u semileptonic decay is distinguished from the b→c background using the hadronic mass MX, the leptonic invariant mass squared q2 and the variable P+≡EX-|p→X|. The results are obtained for events with pl*≥1GeV/c, in three kinematic regions (1)MX 8GeV2/c2, and by (3)P+<0.66GeV/c. The matrix element |Vub| is found to be (4.09±0. 19±0.20-0.15+0.14±0.18)×10-3, where the errors are statistical, systematic including Monte Carlo modeling, theoretical, and from shape function parameter determination, respectively. © 2005 The American Physical Society.