Measurement of the Single Top Quark Production Cross Section in 1.96-TeV Proton-Antiproton Collisions
- Univ. of Tsukuba (Japan)
Top quarks are predominantly produced in pairs via the strong interaction in $$\bar{p}$$p collisions at √s = 1.96 TeV . The top quark has a weak isospin 1/2, composing a weak isospin doublet with the bottom quark. This characteristic predicts not only top quark pair production via strong interaction but also single production together with a bottom quark via weak interaction. However, finding single top quark production is challenging since it is rarely produced (σ singletop = 2.9 pb) against background processes with the same final state like W+jets and t$$\bar{t}$$. A measurement of electroweak single top production probes the W-t-b vertex, which provides a direct determination of the Cabbibo-Kobayashi-Maskawa (CKM) matrix element |Vtb|. The sample offers a source of almost 100% polarized top quarks. This thesis describes an optimized search for s-channel single top quark production and a measurement of the single top production cross section using 2.7 fb-1 of data accumulated with the CDF detector. We are using events with one high-pT lepton, large missing ET and two identified b-quark jets where one jet is identified using a secondary vertex tagger, called SecVtx, and the other jet is identified using SecVtx or a jet probability tagger, called JetProb. In this analysis we have developed a kinematics fitter and a likelihood-based separator between signal and background. As a result, we found that the probability (p-value) that the candidate events originate from a background fluctuation in the absence of single top s-channel production is 0.003, which is equivalent to 2.7 σ deviations in Gaussian statistics, and this excess corresponds to the single top s-channel cross section of 2.38-0.84+1.01 pb. An observed value of |Vtb| is 1.43-0.26+0.38(experimental) ± 0.11(theory). We also set the 95% CL. upper limit of σs = 4.15 pb for the s-channel production cross section.
- Research Organization:
- Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC02-07CH11359
- OSTI ID:
- 952637
- Report Number(s):
- FERMILAB-THESIS-2009-13; TRN: US0902559
- Country of Publication:
- United States
- Language:
- English
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