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Register a new userExclusion of exotic top-like quarks with -4/3 electric charge using jet-charge tagging in single-lepton ttbar events at CDF
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We report on a measurement of the top-quark electric charge in ttbar events in which one W boson originating from the top-quark pair decays into leptons and the other into hadrons. The event sample was collected by the CDF II detector in sqrt(s)=1.96 TeV proton-antiproton collisions and corresponds to 5.6 fb^(-1). We find the data to be consistent with the standard model and exclude the existence of an exotic quark with -4/3 electric charge and mass of the conventional top quark at the 99% confidence level.
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The new CERN proton-proton collider, the LHC, is about to start in 2007 its data taking. Millions of top quarks will be available out of these data, allowing to perform a wide range of precision measurements and searches for new physics. An overview of the planned top physics program accessible with ttbar events is given for the ATLAS and CMS experiments. A particular emphasis is put on the precision measurements of the top mass, top polarization and searches for new physics in top production and decay.
We report evidence for $s$-channel single-top-quark production in proton-antiproton collisions at center-of-mass energy $sqrt{s}= 1.96 mathrm{TeV}$ using a data set that corresponds to an integrated luminosity of $9.4 mathrm{fb}^{-1}$ collected by the Collider Detector at Fermilab. We select events consistent with the $s$-channel process including two jets and one leptonically decaying $W$ boson. The observed significance is $3.8$ standard deviations with respect to the background-only prediction. Assuming a top-quark mass of $172.5 mathrm{GeV}/c^2$, we measure the $s$-channel cross section to be $1.41^{+0.44}_{-0.42} mathrm{pb}$.
The leptonic asymmetry in semileptonic ttbar decays is measured with the CDF detector using the full Tevatron Run II dataset, which corresponds to 9.4 fb^-1 of integrated luminosity. The measured asymmetry is extrapolated to the full kinematic range and the measured value of A_FB^lep = 0.094^+0.032_-0.029 is compared to the NLO prediction A_FB^lep = 0.038 +/- 0.003.
We classify the meson and baryon long lived resonances considering quarks with electric charge 5/3 and $-4/3$ (in units of $vert evert$) predicted by some 3-3-1 models. Some of these exotic resonances have the usual electric charges $0,pm1$, others have $pm(3,4,5)$, and the lightest ones decaying only into leptons plus known resonances. We propose another heavy $SU(3)_H$ global symmetry under which hadrons involving only exotic quarks can be constructed.
We present a measurement of the mass difference between top ($t$) and anti-top ($bar{t}$) quarks using $tbar{t}$ candidate events reconstructed in the final state with one lepton and multiple jets. We use the full data set of Tevatron $sqrt{s} = 1.96$ TeV proton-antiproton collisions recorded by the CDF II detector, corresponding to an integrated luminosity of 8.7 fb$^{-1}$. We estimate event-by-event the mass difference to construct templates for top-quark signal events and background events. The resulting mass difference distribution of data compared to signal and background templates using a likelihood fit yields $Delta M_{top} = {M}_{t} - {M}_{bar{t}} = -1.95 $pm$ 1.11 (stat) $pm$ 0.59 (syst)$ and is in agreement with the standard model prediction of no mass difference.
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