CDF Collaboration(Aaltonen, T. et al), & Cabrera, S. (2010). Exclusion of an Exotic Top Quark with-4/3 Electric Charge Using Soft Lepton Tagging. Phys. Rev. Lett., 105(10), 101801–7pp.
Abstract: We present a measurement of the electric charge of the top quark using p (p) over bar collisions corresponding to an integrated luminosity of 2: 7 fb(-1) at the CDF II detector. We reconstruct t (t) over bar events in the lepton + jets final state. We use soft lepton taggers to determine the flavor of the b jets, which we use to reconstruct the top quark's electric charge and exclude an exotic top quark with -4/3 charge at 95% confidence level. This is the strongest exclusion of the exotic charge scenario and the first to use soft leptons for this purpose.
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CDF Collaboration(Aaltonen, T. et al), & Cabrera, S. (2010). Search for the Production of Scalar Bottom Quarks in p(p)over-bar Collisions at root s=1.96 TeV. Phys. Rev. Lett., 105(8), 081802–7pp.
Abstract: We report on a search for direct scalar bottom quark (sbottom) pair production in p (p) over bar collisions at root s = 1.96 TeV, in events with large missing transverse energy and two jets of hadrons in the final state, where at least one of the jets is required to be identified as originating from a b quark. The study uses a collider detector at Fermilab Run II data sample corresponding to 2.65 fb(-1) of integrated luminosity. The data are in agreement with the standard model. In an R-parity conserving minimal supersymmetric scenario, and assuming that the sbottom decays exclusively into a bottom quark and a neutralino, 95% confidence-level upper limits on the sbottom pair production cross section of 0.1 pb are obtained. For neutralino masses below 70 GeV/c(2), sbottom masses up to 230 GeV/c(2) are excluded at 95% confidence level.
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CDF Collaboration(Aaltonen, T. et al), & Cabrera, S. (2010). Measurement of W-Boson Polarization in Top-Quark Decay in p(p)over-bar Collisions at root s=1.96 TeV. Phys. Rev. Lett., 105(4), 042002–8pp.
Abstract: We report measurements of the polarization of W bosons from top-quark decays using 2.7 fb(-1) of p (p) over bar collisions collected by the CDF II detector. Assuming a top-quark mass of 175 GeV/c(2), three measurements are performed. A simultaneous measurement of the fraction of longitudinal (f(0)) and right-handed (f(0)) W bosons yields the model- independent results f(0) =0. 88 +/- 0.11(stat) +/- 0.06(syst) and f(+) = 0.15 +/- 0.07(stat) +/- 0.06(syst) with a correlation coefficient of -0.59. A measurement of f(0) [f(+)] constraining f(+) [f(0)] to its standard model value of 0.0 [0.7] yields f(0) 0.70 + 0.07(stat) +/- 0.04(syst) [f(+) – 0.01 +/- 0.02(stat) +/- 0.05(syst)]. All these results are consistent with standard model expectations. We achieve the single most precise measurements of f(0) for both the model- independent and modeldependent determinations.
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CDF Collaboration(Aaltonen, T. et al), & Cabrera, S. (2010). Measurement of the Ratio sigma(t(t)over-bar)/sigma(Z/gamma*-> ll) and Precise Extraction of the t(t)over-bar Cross Section. Phys. Rev. Lett., 105(1), 012001–7pp.
Abstract: We report a measurement of the ratio of the t (t) over bar to Z/gamma* production cross sections in root s = 1.96 TeV p (p) over bar collisions using data corresponding to an integrated luminosity of up to 4.6 fb(-1), collected by the CDF II detector. The t (t) over bar cross section ratio is measured using two complementary methods, a b-jet tagging measurement and a topological approach. By multiplying the ratios by the well-known theoretical Z/gamma* -> ll cross section predicted by the standard model, the extracted t (t) over bar cross sections are effectively insensitive to the uncertainty on luminosity. A best linear unbiased estimate is used to combine both measurements with the result sigma(t (t) over bar) = 7.70 +/- 0.52 pb, for a top-quark mass of 172.5 GeV/c(2).
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CDF Collaboration(Aaltonen, T. et al), & Cabrera, S. (2010). Direct Top-Quark Width Measurement at CDF. Phys. Rev. Lett., 105(23), 232003–7pp.
Abstract: We present a measurement of the top-quark width in the lepton + jets decay channel of t (t) over bar events produced in p (p) over bar collisions at Fermilab's Tevatron collider and collected by the CDF II detector. From a data sample corresponding to 4.3 fb(-1) of integrated luminosity, we identify 756 candidate events. The top-quark mass and the mass of the hadronically decaying W boson that comes from the top-quark decay are reconstructed for each event and compared with templates of different top-quark widths (Gamma(t)) and deviations from nominal jet energy scale (Delta(JES)) to perform a simultaneous fit for both parameters, where Delta(JES) is used for the in situ calibration of the jet energy scale. By applying a Feldman-Cousins approach, we establish an upper limit at 95% confidence level (CL) of Gamma(t) < 7.6 GeV and a two-sided 68% CL interval of 0.3 GeV < Gamma(t) < 4.4 GeV for a top-quark mass of 172.5 GeV/c(2), which are consistent with the standard model prediction.
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