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

Thesis/Dissertation · Tue Dec 01 00:00:00 EST 2009

DOI:https://doi.org/10.2172/970067· OSTI ID:970067

Liu, Zhiyi ^[1]

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1. China Inst. of Atomic Energy (CIAE), Beijing (China)

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_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^-1 of Tevatron Run II data in p$$\bar{p}$$ collisions at √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_-1.8^+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 σ(p$$\bar{p}$$ → tb + X,tqb + X) = 3.84_-0.83^+0.89 pb. A lower limit on |V_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.

• Research Organization: Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC02-07CH11359
• OSTI ID: 970067
• Report Number(s): FERMILAB-THESIS-2009-45; TRN: US1000730
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
CROSS SECTIONS
ELECTRONS
FERMILAB TEVATRON
HADRONS
MATRIX ELEMENTS
MUONS
PHYSICS
PRODUCTION
SENSITIVITY
STANDARD MODEL
T QUARKS
TAU PARTICLES
TREES
WEAK INTERACTIONS
single top quark
electroweak top quark
tau lepton
tau+jets channel
cross section
Tevatron
D0
boosted decision trees