A measurement of the partial width ratio GAMMA(bbBAR)/GAMMA(had) using a method which tags the Z --> bbBAR decays through the lifetime 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 GAMMA(bbBAR)/GAMMA(had) 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 GAMMA(bbBAR)/GAMMA(had) = 0.2192+/-0.0022(stat.)+/-0.0026(syst.)+/-0.0016(GAMMA(ccBAR)/GAMMA(had)) is found. Combining this result with other recent ALEPH GAMMA(bbBAR)/GAMMA(had) measurements gives a 95% confidence upper limit on the Standard Model top mass of M(t) < 228 GeV.
A PRECISE MEASUREMENT OF GAMMA-Z-]B(B)BAR/GAMMA-Z-] HADRONS
SELVAGGI, Giovanna;DE PALMA, Mauro;NUZZO, Salvatore Vitale
1993-01-01
Abstract
A measurement of the partial width ratio GAMMA(bbBAR)/GAMMA(had) using a method which tags the Z --> bbBAR decays through the lifetime 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 GAMMA(bbBAR)/GAMMA(had) 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 GAMMA(bbBAR)/GAMMA(had) = 0.2192+/-0.0022(stat.)+/-0.0026(syst.)+/-0.0016(GAMMA(ccBAR)/GAMMA(had)) is found. Combining this result with other recent ALEPH GAMMA(bbBAR)/GAMMA(had) measurements gives a 95% confidence upper limit on the Standard Model top mass of M(t) < 228 GeV.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
