Measurement of Top Quark Properties and Search for the Standard Model Higgs Boson in Proton Anti-Proton Collisions at $$\sqrt{s}$$ = 1.96 TeV
- Waseda Univ., Shinjuku (Japan)
We present a measurement of the top quark mass and of the top-antitop ( tf) pair production cross section and a search for the Standard Model Higgs boson with CDF II Detector in pp collisions at $$\sqrt{s}$$ = 1.96 TeV. The integrated luminosity of 2.9 $$fb^{-1}$$ is used for top-antitop pair production cross section and top quark mass measurement. We adopt a neural-network algorithm to select candidate events from six or more jets. At least one of these jets should be required to be b jet, as identified by the reconstruction of a secondary vertex inside the jet. The mass measurement is based on a likelihood fit incorporating reconstructed mass distributions representative of signal and background, where the absolute jet energy scale (JES) is measured simultaneously with the top quark mass. The measurement yields a value of 174.8 ± 2.4 (stat + JES) $$^{+1.2}_{-1.0}$$ (syst) GeV/$c^2$ , where the uncertainty from the absolute jet energy scale is evaluated together with the statistical uncertainty. The procedure also measures the amount of signal from which we derive a cross section, $$\sigma_{t\bar{t}}$$ = 7.2 ± 0.5 (stat) ±1.0 (syst) ± 0.4 (lum) $pb$, for the measured values of top quark mass and JES. Top quark mass and W boson mass constrain the mass of the Standard Model Higgs boson, indirectly. This prediction implies MH = 89 $$^{+35}_{-26}$$GeV/$c^2$ (68% confidence level) as of July 2010. Therefore, we concentrate on the Standard Model Higgs mass search region with $$\le$$ 135 GeV / $c^2$ . Then, we search for the Standard Model Higgs boson associated with vector boson using the decay modes consisting of leptons only: Signal processes are $$WH \to \ell \nu + \tau\tau$$ and $$ZH \to l l + \tau \tau$$. We simply select 3 or 4 lepton including hadronic T to pick candidate events out. To improve search sensitivity, we adopt Support Vector Machine to discriminate signals from backgrounds. Using about 6.2 $$fb^{-1}$$ data, there was no clear discrepancy between data and our background estimation. Therefore, we extract cross section upper limit of the Standard Model Higgs production at 95 % confidence level. The observed upper limit on assumption of $$M_H$$ = 115 GeV/$c^2$ is 25.1 x $$\sigma^{SM}$$ at 95% confidence level while the expectation is 17.3 x $$\sigma ^{SM}$$ at 95%.
- Research Organization:
- Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), High Energy Physics (HEP)
- DOE Contract Number:
- AC02-07CH11359
- OSTI ID:
- 1353471
- Report Number(s):
- FERMILAB-THESIS-2011-71; 1516537
- Country of Publication:
- United States
- Language:
- English
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