Search for the Top Quark in the Electron + Jets + Soft Muon Channel at D0

Thesis/Dissertation · Wed May 01 04:00:00 EDT 1996

DOI:https://doi.org/10.2172/1421762· OSTI ID:1421762

Xu, Haowei ^[1]

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1. Brown U.

The top quark is required in the standard model as the weak isospin partner of the b quark and is the only unobserved quark in three generations of quarks. At the Tevatron, the top quark is expected to be produced in pairs via the strong interactions. Almost all top quarks will decay into a b quark and a W boson, which decays in tum to pairs of leptons or quarks. In this analysis, we concentrated on the electron +jets final state where one W decays into an electron and neutrino and the other W decays into a pair of quarks. To suppress the background arising from production of a high-PT W accompanied by jets, we tagged the b quarks through their semileptonic decays with muons in the final state. This thesis includes detailed discussions on the W + jet event identification, muon tagging criteria, background estimates, and efficiency studies. Based on a data sample with integrated luminosity of 13.5 ± 1.6 $$pb^{-1}$$ from the 1992-93 running period, two $$t\bar{t}$$ candidate events were observed with an expected background of 0.60 ± 0.15 events, which yields a small excess of events over expected background. In combination with all D0 top quark analyses with approximately 50 $$pb^{-1}$$ of data accumulated by the D0 detector during the period 1992-1995, we observed 17 events with an expected background of 3.9 ± 0.6. The probability of an upward fluctuation of the background to 17 or more events is 2x$$l0^{-6}$$. This leads to the conclusion that production of the top quark has been observed in pjj collisions with a center of mass energy of 1.8 Te V.

• Research Organization: Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
• DOE Contract Number: AC02-07CH11359
• OSTI ID: 1421762
• Report Number(s): FERMILAB-THESIS-1996-24; D0-NOTE-2744; UMI-97-04159; 429287
• Country of Publication: United States
• Language: English

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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS