A measurement of using a double tagging method
The OPAL Collaboration
G.Abbiendi 2 - et al.
2Dipartimento di Fisica dell' Università di Bologna and INFN, I-40126 Bologna, Italy
Received: 28 August 1998 / Published online: 7 April 1999
The fraction of events in hadronic decays has been measured by the OPAL experiment using the data collected at LEP between 1992 and 1995. The decays were tagged using displaced secondary vertices, and high momentum electrons and muons. Systematic uncertainties were reduced by measuring the b-tagging efficiency using a double tagging technique. Efficiency correlations between opposite hemispheres of an event are small, and are well understood through comparisons between real and simulated data samples. A value of
was obtained, where the first error is statistical and the second systematic. The uncertainty on , the fraction of events in hadronic decays, is not included in the errors. The dependence on is
where is the deviation of from the value 0.172 predicted by the Standard Model. The result for agrees with the value of predicted by the Standard Model.