observation of t-channel electroweak top quark production

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Triplett, Nathan
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James Cochran
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Physics and Astronomy
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The top quark is the heaviest known fundamental particle, with a mass of 172.0 +0.9 -1.3 GeV. This is nearly twice the mass of the second heaviest known particle, the Z boson, and roughly the mass of a gold atom. Because of its unusually large mass, studying the top quark may provide insight into the Higgs mechanism and other beyond the standard model physics.

Only two accelerators in the world are powerful enough to produce top quarks. The Tevatron, which first accelerated protons in 1983, has produced almost 400,000 top quarks, roughly half at each of its two detectors: D0 and CDF. The LHC is a much newer accelerator which currently has accumulated about 0.5% as much data as the Tevatron. However, when running at full luminosity, the LHC is capable of producing a top quark about once every second and will quickly surpass the Tevatron as the leading producer of top quarks. This analysis uses data from the D0 detector at the Tevatron, which are described in chapter.

Top quarks are produced most often in pairs of top and anti-top quarks through an interaction of the strong force. This production mode was first observed in 1995 at the Tevatron. However, top quarks can also be produced though an electroweak interaction, which produces just one top quark. This production mode was first observed at the Tevatron in 2008 \cite{prl-obs}. Single top quark production can occur in different channels. In this analysis, a measurement of the cross section of the t-channel production mode is performed. This measurement uses 5.4 fb-1 of data and uses the technique of boosted decision trees in order to separate signal from background events. The t-channel cross section is measured to be:

σ(ppbar → tqb + X) = 3.03 +0.78 -0.66 pb

Additional cross section measurements were also performed for the s-channel as well as the s+t-channel. The measurement of each one of these three cross sections was repeated three times using different techniques, and all three methods were combined into a "super-method" which achieves the best performance. The details of these additional measurements are shown in appendix A.

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Sat Jan 01 00:00:00 UTC 2011