Measurements of Z 0 → heavy flavours at LEP

Abstract

The LEP experiments have studied the decays of the Z 0 to heavy quarks by exploiting their semi-leptonic decays, characteristic decay topology and lifetime, and by identifying inclusive and exclusive production of heavy flavoured hadrons. The emphasis here is placed on the measurement of the fraction of hadronic decays containing b or c quark decays to leptons, for which the LEP average values are: Γ b b Γ had × B(b→1)=0.0239±0.0007±0.0007 Γ c c Γ had × B(c→1)=0.0161±0.0015±0.0014 where the first error is statistical and the second systematic. The average partial widths derived from these measurements are: Γ b b =355±9±10±18( BR)MeV Γ c c =292±29±18( BR)MeV where systematic errors are dominated by the uncertainty in the semi-leptonic branching ratio. These results are in good agreement with the standard model expectations Γ b b = 378 MeV and Γ c c = 297 MeV , but the experimental accuracy is at present insufficient to confront detailed predictions such as the variation with top quark mass.