A measurement of the partial width ratio Γbb/Γhad using a method which tags the Z --> bb decays through the lif etime of the produced heavy hadrons is presented. This method relies on the tracking precision afforded by a double-sided silicon vertex detector. The tag algorithm makes a probabilistic interpretation of three-dimensional track impact parameters, using the data to measure the resolution. By tagging the two b hadrons separately, both Γbb/Γhad and the tag efficiency can be determined from the data. For a 26% efficiency of tagging a single b hadron within the vertex detector solid angle coverage, a purity of 96% is achieved. A value of Γbb/Γhad = 0.2192+/-0.0026(stat.)+/-0.0016(Γcc/ Γhad) is found. Combining this result with other recent ALEPH Γbb/Γhad measurements gives a 95% confidence upper limit on the Standard Model top mass of Mt < 228 GeV.

A precise measurement of ΓZ→bb/ΓZ→hadrons

GREGORIO, ANNA;BOSISIO, LUCIANO;GIANNINI, GIANROSSANO;
1993-01-01

Abstract

A measurement of the partial width ratio Γbb/Γhad using a method which tags the Z --> bb decays through the lif etime of the produced heavy hadrons is presented. This method relies on the tracking precision afforded by a double-sided silicon vertex detector. The tag algorithm makes a probabilistic interpretation of three-dimensional track impact parameters, using the data to measure the resolution. By tagging the two b hadrons separately, both Γbb/Γhad and the tag efficiency can be determined from the data. For a 26% efficiency of tagging a single b hadron within the vertex detector solid angle coverage, a purity of 96% is achieved. A value of Γbb/Γhad = 0.2192+/-0.0026(stat.)+/-0.0016(Γcc/ Γhad) is found. Combining this result with other recent ALEPH Γbb/Γhad measurements gives a 95% confidence upper limit on the Standard Model top mass of Mt < 228 GeV.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11368/2563434
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