The b semileptonic branching ratio in decays

Abstract

Publisher Summary This chapter presents the measurement of the inclusive semileptonic branching fraction of b hadrons from the large electron–positron (LEP) experiments. Measuring b hadrons involves identifying lepton candidates in samples enriched in Z 0 → b b ¯ decays; b-tagging is performed with algorithms that exploit the long lifetime and heavy mass of b quarks. A double-tag technique is typically used to measure the tagging purity directly from the data. To measure the two branching ratios, the different sources of prompt leptons in heavy flavor decays need to be disentangled, as well as separated, from non-prompt leptons (K and π decays in flight) and background (hadrons misidentified as leptons) produced in events of all flavors. Several strategies have been used by the four LEP Collaborations to separate the different sources of lepton candidates and extract the signal. The direct and cascade decay branching ratios can be measured from a fit to the p and p⊥ spectra of the reconstructed leptons.