Measurement of the Polarized Forward-backward Asymmetry of B Quarks Using Momentum-weighted Track Charge at SLD. PDF Download

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Languages : en
Pages : 132

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Book Description
This thesis presents a direct measurement of the parity-violating parameter A{sub b} by analyzing the polarized forward-backward asymmetry of b quarks in ee− --> Z° --> b{bar b}. Data were taken at the Stanford Linear Accelerator Center (SLAC), with the Stanford Large Detector (SLD), which records the products of ee− interactions at a center of mass energy (square root)s = 91.2 GeV/c2 at the SLAC Linear Collider (SLC). The SLC/SLD experimental apparatus provides a unique and ideal environment for measuring electroweak asymmetries. Heavy flavor decays of the Z° were identified inclusively by taking advantage of the long lifetime of B hadrons, the small, stable SLC beam spot, and SLD's precise tracking detectors. Two analysis techniques for measuring A{sub b} are presented: a binned fit to the left-right forward-backwards asymmetry of tagged events signed with momentum-weighted track charge, and a self-calibrating maximum-likelihood technique using momentum-weighted charge from the two hemispheres in each tagged event. From our 1994-1995 sample of 3.6 pb−1, having a luminosity-weighted average e− polarization of 77.3%, and our 1993 sample of 1.8 pb−1, having a luminosity-weighted polarization of 63.1%, we obtain A{sub b} = 0.848 " 0.046(stat.) " 0.050(syst.).