Measurement of electroweak single top quark production in proton-antiproton collisions at 1.96 TeV

Abstract

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 |V tb|, and measurement of the single top quark production cross section is currently the only method to directly measure this quantity without assuming the number of generations of fermions. This thesis describes a measurement of the cross section of electroweak single top quark production in proton-antiproton collisions at a center-of-mass energy of 1.96 TeV. This analysis uses 2.2 fb-1 of integrated luminosity recorded by the Collider Detector at Fermilab. The search is performed using a matrix element method which calculates the differential cross section for each event for several signal and background hypotheses. These numbers are combined into a single discriminant and used to construct templates from Monte Carlo simulation. A maximum likelihood fit to the data distribution gives a measurement of the cross section. This analysis measures a value of 2.2$+0.8\atop{-0.7}$ pb, which corresponds to a value of |V tb| = 0.88$+0.16\atop{-0.14}$experimental±0.7(theoretical). The probability that this result originates from a background fluctuation in the absence of single top production (p-value) is 0.0003, which is equivalent to 3.4 standard deviations in Gaussian statistics. The expected (median) p-value as estimated from pseudo-experiments for this analysis is 0.000003, which corresponds to 4.5 standard deviations in Gaussian statistics.