Measurement of the absolute value of V,(ub) using b semileptonic decay

The magnitude of the CKM matrix element |V_ub| is determined by measuring the inclusive charmless semileptonic branching fraction of beauty hadrons at OPAL based on b → X_uℓν event topology and kinematics. This analysis uses OPAL data collected between 1991 and 1995, which correspond to about four million hadronic Z decays. Br( b → X_uℓν) is measured to be [special characters omitted]. The first uncertainty is the statistical error and the second is the systematic error. From this analysis, |V_ub| is determined to be: [special characters omitted]The last error represents the theoretical uncertainties related to the extraction of |V_ub| from Br(b → X_uℓν) using the Heavy Quark Expansion.