Determination of $\mid V_{ub} \mid$ from the Measurement of the Inclusive Charmless Semileptonic Branching Ratio of b hadrons

Abstract

From a study of the kinematic properties of the final state produced in the semileptonic decays b-->X l nu, the inclusive charmless semileptonic branching ratio of b hadrons is measured. With a sam ple of 3.6 million hadronic Z decays recorded between 1992 and 1995 with the ALEPH detector at LEP, the value Br(b-->X_u l nu) is determined to be (1.73 +- 0.55_stat +- 0.55_syst)*10^{-3}, where X_u represents any charmless hadronic state and b is a mixture of b hadrons weighted by their production rates. This measurement yields the result |V_ub|^2= (18.68 +- 5.94_stat +- 5.94_syst +- 1 .45_HQE)*10^{-6}, where the last error comes from the conversion of the branching ratio to the CKM matrix element squared