2,061 research outputs found

    A search for t -> tau nu q in t(t)over-bar production

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    We present a search for t over(t, ̄) events with a tau lepton in the final state. The data sample corresponds to an integrated luminosity of 194 pb-1 collected with the CDF II detector from p over(p, ̄) collisions at a center of mass energy of 1.96 TeV. We observe two events with an expected signal of 1.0 ± 0.2 events and a background of 1.3 ± 0.3 events. We determine a 95% confidence level upper limit on rτ, the ratio of the measured rate of t → τ ν q to the expectation, of 5.2. © 2006 Elsevier B.V. All rights reserved

    First Measurement of the t(t) over bar Differential Cross Section d sigma/dM(t(t) over bar) in p(p) over bar Collisions at root s=1.96 TeV

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    We present a measurement of the t(t) over bar differential cross section with respect to the t(t) over bar invariant mass, d sigma/dM(t(t) over bar), in p(p) over bar collisions at root s=1.96 TeV using an integrated luminosity of 2.7 fb(-1) collected by the CDF II experiment. The t(t) over bar invariant mass spectrum is sensitive to a variety of exotic particles decaying into t(t) over bar pairs. The result is consistent with the standard model expectation, as modeled by PYTHIA with CTEQ5L parton distribution functions

    Measurement of the Ratio sigma(t(t)over-bar)/sigma(Z/gamma*-> ll) and Precise Extraction of the t(t)over-bar Cross Section

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    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)

    Search for a technicolor omega(T) particle in events with a photon and a b-quark jet at Fermilab

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    If the technicolor wr particle exists, a likely decay mode is omega(T) --> gamma pi(T), followed by pi(T) --> b (b) over bar, yielding the signature gamma b (b) over bar. We have searched 85 pb(-1) of data collected by the CDF experiment at the Fermilab Tevatron for events with a photon and two jets, where one of the jets must contain a secondary vertex implying the presence of a b quark. We find no excess of events above standard model expectations. We express the result as an exclusion region in the M-omega T-M-pi T mass plane

    Measurement of the Mass Difference between t and (t)over-bar Quarks

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    We present a direct measurement of the mass difference between t and (t) over bar quarks using t (t) over bar candidate events in the lepton + jets channel, collected with the CDF II detector at Fermilab's 1.96 TeV Tevatron p (p) over bar Collider. We make an event by event estimate of the mass difference to construct templates for top quark pair signal events and background events. The resulting mass difference distribution of data is compared to templates of signals and background using a maximum likelihood fit. From a sample corresponding to an integrated luminosity of 5.6 fb(-1), we measure a mass difference, Delta M-top = M-t - M-(t) over bar = - 3:3 +/- 1.4(stat) +/- 1.0(syst) GeV/c(2), approximately 2 standard deviations away from the CPT hypothesis of zero mass difference

    Measurement of the top quark p(T) distribution

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    We have measured the p(T) distribution of top quarks that are pair produced in p (p) over bar collisions at roots = 1.8 TeV using a sample of t (t) over bar decays in which we observe a single high-P-T charged lepton, a neutrino, and four or more jets. We use a likelihood technique that corrects for the experimental bias introduced due to event reconstruction and detector resolution effects. The observed distribution is consistent with the standard model prediction. We use these data to place limits on the production of high-p(T) top quarks suggested in some models of anomalous top quark pair production

    Measurement of B(t -> Wb)/B(t -> Wq) at the Collider Detector at Fermilab

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    We present a measurement of the ratio of top-quark branching fractions R=B(t -> Wb)/B(t -> Wq), where q can be a b, s, or a d quark, using lepton-plus-jets and dilepton data sets with an integrated luminosity of similar to 162 pb(-1) collected with the Collider Detector at Fermilab during Run II of the Tevatron. The measurement is derived from the relative numbers of t (t) over bar events with different multiplicity of identified secondary vertices. We set a lower limit of R > 0.61 at 95% confidence level

    Cross section measurements of high-p(T) dilepton final-state processes using a global fitting method

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    We present a new method for studying high-p(T) dilepton events (e(+/-)e(-/+), mu(+/-)mu(-/+), e(+/-)mu(-/+)) and simultaneously extracting the production cross sections of p (p) over bar -\u3e t (t) over bar, p (p) over bar -\u3e W+W-, and p (p) over bar -\u3e Z(0) -\u3e tau(+)tau(-) at a center-of-mass energy of root s = 1.96 TeV. We perform a likelihood fit to the dilepton data in a parameter space defined by the missing transverse energy and the number of jets in the event. Our results, which use 360 pb(-1) of data recorded with the CDF II detector at the Fermilab Tevatron Collider, are sigma(t (t) over bar) = 8.5(-2.2)(+2.7) pb, sigma(W+W-) = 16.3(-4.4)(+5.2) pb, and sigma(Z(0) -\u3e tau(+)tau(-)) = 291(-46)(+50) pb

    Measurement of the t(t)over-bar production cross section in p(p)over-bar collisions at root s=1.8 TeV

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    We update the measurement of the t (t) over bar production cross section using the CDF detector at the Fermilab Tevatron. This measurement uses t (t) over bar decays to the final states e + nu + jets and mu + nu + jets. We search for b quarks from t decays via secondary-vertex identification or the identification of semileptonic decays of the b and cascade c quarks. The background to the t (t) over bar production is determined primarily through a Monte Carlo simulation. However, we calibrate the simulation and evaluate its uncertainty using several independent data samples. For a top quark mass of 175 GeV/c(2), we measure sigma (t (t) over bar)-=5.1 +/- 1.5 pb and sigma (t (t) over bar)=9.2 +/- 4.3 pb using the secondary vertex and the lepton tagging algorithms, respectively. Finally, we combine these results with those from other t (t) over bar decay channels and obtain sigma (t (t) over bar)-= 6.5 (+1.7)(-1.4)p
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