Measurements of Γ(ZO → b bar b)/Γ(ZO → hadrons) using the SLD

The quantity Rb = Γ(Zo →b bar b)/Γ(Zo → hadrons) is a sensitive measure of corrections to the Zbb vertex. The precision necessary to observe the top quark mass dependent corrections is close to being achieved. LEP is already observing a 1.8σ deviation from the Standard Model prediction. Knowledge of the top quark mass combined with the observation of deviations from the Standard Model prediction would indicate new physics. Models which include charged Higgs or light SUSY particles yield predictions for Rb appreciably different from the Standard Model. In this thesis two independent methods are used to measure Rb. One uses a general event tag which determines Rb from the rate at which events are tagged as Zo → b bar b in data and the estimated rates at which various flavors of events are tagged from the Monte Carlo. The second method reduces the reliance on the Monte Carlo by separately tagging each hemisphere as containing a b-decay. The rates of single hemisphere tagged events and both hemisphere tagged events are used to determine the tagging efficiency for b-quarks directly from the data thus eliminating the main sources of systematic error present in the event tag. Both measurements take advantage of the unique environment provided by the SLAC Linear Collider (SLC) and the SLAC Large Detector (SLD). From the event tag a result of Rb = 0.230±0.004statistical±0.013systematic is obtained. The higher precision hemisphere tag result obtained is Rb = 0.218±0.004statistical±0.004systematic±0.003Rc