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 $1.63\pm 0.53+0.55-0.62\times 10-3$. The first uncertainty is the statistical error and the second is the systematic error. From this analysis, |V_ub| is determined to be: &vbm0;Vub&vbm0;=&parl0; 4.00±0.65stat ^+0.67-0.76 sys±0.19 HQE&parr0;×10^-3 . The last error represents the theoretical uncertainties related to the extraction of |V_ub| from Br(b → X_uℓν) using the Heavy Quark Expansion.