Measurement of single top quark production in the tau+jets channnel using boosted decision trees at D0

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The top quark is the heaviest known matter particle and plays an important role in the Standard Model of particle physics. At hadron colliders, it is possible to produce single top quarks via the weak interaction. This allows a direct measurement of the CKM matrix element V{sub tb} and serves as a window to new physics. The first direct measurement of single top quark production with a tau lepton in the final state (the tau+jets channel) is presented in this thesis. The measurement uses 4.8 fb{sup -1} of Tevatron Run II data in p{bar p} collisions at {radical}s = 1.96 ... continued below

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235 pages

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Liu, Zhiyi & U., /Simon Fraser December 1, 2009.

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The top quark is the heaviest known matter particle and plays an important role in the Standard Model of particle physics. At hadron colliders, it is possible to produce single top quarks via the weak interaction. This allows a direct measurement of the CKM matrix element V{sub tb} and serves as a window to new physics. The first direct measurement of single top quark production with a tau lepton in the final state (the tau+jets channel) is presented in this thesis. The measurement uses 4.8 fb{sup -1} of Tevatron Run II data in p{bar p} collisions at {radical}s = 1.96 TeV acquired by the D0 experiment. After selecting a data sample and building a background model, the data and background model are in good agreement. A multivariate technique, boosted decision trees, is employed in discriminating the small single top quark signal from a large background. The expected sensitivity of the tau+jets channel in the Standard Model is 1.8 standard deviations. Using a Bayesian statistical approach, an upper limit on the cross section of single top quark production in the tau+jets channel is measured as 7.3 pb at 95% confidence level, and the cross section is measured as 3.4{sub -1.8}{sup +2.0} pb. The result of the single top quark production in the tau+jets channel is also combined with those in the electron+jets and muon+jets channels. The expected sensitivity of the electron, muon and tau combined analysis is 4.7 standard deviations, to be compared to 4.5 standard deviations in electron and muon alone. The measured cross section in the three combined final states is {sigma}(p{bar p} {yields} tb + X,tqb + X) = 3.84{sub -0.83}{sup +0.89} pb. A lower limit on |V{sub tb}| is also measured in the three combined final states to be larger than 0.85 at 95% confidence level. These results are consistent with Standard Model expectations.

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235 pages

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  • Report No.: FERMILAB-THESIS-2009-45
  • Grant Number: AC02-07CH11359
  • DOI: 10.2172/970067 | External Link
  • Office of Scientific & Technical Information Report Number: 970067
  • Archival Resource Key: ark:/67531/metadc930153

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Office of Scientific & Technical Information Technical Reports

Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

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  • December 1, 2009

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  • Nov. 13, 2016, 7:26 p.m.

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  • Dec. 7, 2016, 4:57 p.m.

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Liu, Zhiyi & U., /Simon Fraser. Measurement of single top quark production in the tau+jets channnel using boosted decision trees at D0, thesis or dissertation, December 1, 2009; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc930153/: accessed April 24, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.