Measurement of the W boson+bottom-antibottom quark cross-section in 695 pb-1 of proton-antiproton collisions at CDF II.

Abstract

<italic>W</italic><super>+/-</super>+ <italic>bb&macr;</italic> events contain the associated production of a <italic>W</italic><super>+/- </super> boson, a pair of bottom quarks (<italic>bb&macr;</italic>), and any number of additional partons. This process is of much importance at hadron collider experiments due to its role as a background source in searches for Standard Model Higgs boson and single top-quark production. In this thesis the results are presented for a measurement of the <italic>b</italic>-jet cross-section in <italic>W</italic><super>+/-</super>+<italic>bb&macr; </italic> events containing 1 or 2 jets in 695 pb<super>-1</super> of s =1.96 TeV <italic>pp&macr;</italic> collisions at the CDF experiment. This is the first measurement of the cross-section of <italic>W</italic><super> +/-</super>+<italic>bb&macr;</italic> performed in any experiment. The cross-section is defined to be proportional to the number of <italic>b</italic>-jets from <italic>W</italic><super>+/-</super>+<italic>bb&macr;</italic> events with one or two jets, and a leptonically decaying <italic>W</italic><super> +/-</super> with decay products passing kinematics cuts (<italic>p_T</italic>(&ell;<super>+/-</super>) &ge;20.0 GeV, |eta(&ell;<super> +/-</super>)| &le;1.1, <italic>p_T</italic>(nu) &ge;25.0 GeV). The invariant mass distribution of jets identified as containing a long-lived hadron is fit with components for bottom, charm, and light-flavor to find the fraction due to true <italic>b</italic>-decays. Background <italic>b</italic>-jet sources are subtracted to isolate the contribution of <italic>W</italic><super> +/-</super>+<italic>bb&macr;</italic> to the data. The cross-section is measured to be 0.90+/-0.20(stat.)+/-0.26(syst.)pb, which compares well with the leading order theoretical prediction of 0.74+/-0.18 pb.