Measurement of Vub using b hadron semileptonic decay.

The magnitude of the CKM matrix element \(|{\rm V}_{\rm ub}|\) is determined by measuring the inclusive charmless semileptonic branching fraction of beauty hadrons at OPAL based on \(b \to{\rm X}_{\rm u} \ell \nu \) event topology and kinematics. This analysis uses OPAL data collected between 1991 and 1995, which correspond to about four million hadronic Z decays. We measure Br(\(b \to{\rm X}_{\rm u} \ell \nu\)) 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, \(|{\rm V}_{\rm ub}|\) is determined to be: