The top quark is an extremely massive fundamental particle that is predominantly produced in pairs at particle collider experiments. The Standard Model of particle physics predicts that top quarks can also be produced singly by the electroweak force; however, this process is more difficult to detect because it occurs at a smaller rate and is more difficult to distinguish from background processes. The cross section of this process is related to the Cabbibo-Kobayashi-Maskawa matrix element.

Top quarks are predominantly produced in pairs via the strong interaction in {bar p}p collisions at √s = 1.96 TeV . The top quark has a weak isospin 1/2, composing a weak isospin doublet with the bottom quark. This characteristic predicts not only top quark pair production via strong interaction but also single production together with a bottom quark via weak interaction. However, finding single top quark production is challenging since it is rarely produced ([sigma]{sub singletop} = 2.9 pb) against background processes with the same final state like W+jets and t{bar t}. A measurement of electroweak single top production probes the W-t-b vertex, which provides a direct determination of the Cabbibo-Kobayashi-Maskawa (CKM) matrix element.

We present a new model-independent measurement of the electroweak single top-quark production cross section in proton-antiproton (p- $\bar{p}$) collisions at √s = 1.96 TeV in 9.7 fb-1 of integrated luminosity collected with the DØ detector.

This thesis describes the first search for electroweak single top quark production in proton-antiproton collisions at a center of mass energy of 1.96 TeV. The data sample used for this analysis corresponds to 162 pb{sup -1} recorded by the upgraded Collider Detector at Fermilab. The search is performed by doing a classic maximum likelihood fit to the H{sub T} distribution in data. The kinematic variable H{sub T} is the scalar sum of transverse energies of all final state particles in the event. This variable has the advantage that its distribution looks very similar for both contributing (s-channel and t-channel) single top processes, but is different for background processes. The combination of both channels to one signal improves the sensitivity of the search. No significant evidence for electroweak single top quark production is found and we set an upper limit at the 95% confidence level on the combined single top quark production cross section of 17.8 pb.

This thesis describes the first search for electroweak single top quark production in proton-antiproton collisions at a center of mass energy of 1.96 TeV. The data sample used for this analysis corresponds to 162 pb -1 recorded by the upgraded Collider Detector at Fermilab. The search is performed by doing a classic maximum likelihood fit to the H T distribution in data. The kinematic variable H T is the scalar sum of transverse energies of all final state particles in the event. This variable has the advantage that its distribution looks very similar for both contributing (s-channel and t-channel) single top processes, but is different for background processes. The combination of both channels to one signal improves the sensitivity of the search. No significant evidence for electroweak single top quark production is found and we set an upper limit at the 95% confidence level on the combined single top quark production cross section of 17.8 pb.

"We present a new model-independent measurement of the electroweak single top-quark production cross section in proton-antiproton collisions at [radical]s = 1:96 TeV in 9.7 fb-1 of integrated luminosity collected with the D[Zero] detector. Top quarks can be produced singly through the electroweak interaction when an off-sell (virtual) W boson in the s-channel decays to tb quarks ("tb" final state), or through the fusion of a virtual W boson with an incident virtual b quark in the t-channel to produce a top quark associated with a b and a first-generation quarks ("tqb" final state). We select signal-like events, containing one energetic electron or muon, an imbalance in transverse momentum, and two or three jets, with one or two identified as candidates for originating from the fragmentation of b quarks. A discriminant based on the "Matrix Element" method is used to separate the signal from background, and a Bayesian approach is utilized to extract the cross sections for signals. The s and t-channel cross sections are extracted simultaneously, providing a way to measure both modes without assuming the Standard Model prediction for either. The s and t-channel cross sections for producing a single top quark are measured to be [Formulas would not render]. The probabilities to measure these values or larger of cross section in absence of signal are 4.0 x 10-4 for the s-channel and 3.1 x 10-6 for the t-channel, corresponding, respectively, to 3.4 and 4.5 standard deviation significance. These results are among the most accurate measurements to date, and are consistent with the expectations of the Standard Model of 1.04 [plus or minus] 0.08 and 2.26 [plus or minus] 0.2 pb, respectively"--Abstract.