Measurement of the s-channel Single Top Quark Cross Section at the CDF Experiment and Contributions to the Evidence of H->bb at the Tevatron

Liu, Hao, Physics - Graduate School of Arts and Sciences, University of Virginia
Group, Robert, Department of Physics, University of Virginia

In this thesis, we present the measurement of the s-channel single top quark production cross section. In the cross section measurement we use data generated by proton-antiproton collisions at the center-of-mass energy $\sqrt{s}= 1.96$ TeV and collected by the CDF Run II detector. The total data set corresponds to an integrated luminosity of 9.4 fb^-1. We select events consistent with the s-channel process including two jets identified as originating from b quarks and one leptonically decaying W boson. The observed significance is 3.8 standard deviations with respect to the background-only hypothesis. Assuming a top-quark mass of 172.5 GeV/c^2, we measure the s-channel cross section to be 1.41^{+0.44}_{-0.42} pb. When combined with other measurements at the CDF and D0 experiments, the observed significance increases to 6.4 standard deviations, which is interpreted as the first observation of the single top quark s-channel production process.

While the s-channel measurement is the centerpiece of this thesis, the author also contributed to the Higgs boson search. The techniques of the single top quark analysis were adapted from the search for the standard model Higgs boson produced in association with a W boson, since these two processes have the same final-state particles. The author's improvements implemented in the WH search are also described, and the final Higgs boson results are reported. 95% credibility level upper limits are set on the WH production cross section times the H-> bb branching ratio as a function of the Higgs boson mass hypothesis. First evidence of the H->bb process is also found when all searches in this Higgs boson decay mode from the CDF and D0 experiments are combined.

PHD (Doctor of Philosophy)
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