1,157 research outputs found

    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

    Observation of hadronic W decays in t(t)over-bar events with the Collider Detector at Fermilab

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    We observe hadronic W decays in t (t) over bar --> W(--> l nu) + greater than or equal to 4 jet events using a 109 pb(-1) data sample of p (p) over bar collisions at root s = 1.8 TeV collected with the Collider Detector at Fermilab. A peak in the dijet invariant mass distribution is obtained that is consistent with W decay and inconsistent with the background prediction by 3.3 sigma. From this peak we measure the W mass to be 77.2 +/- 4.6(stat + syst) GeV/c(2). This result demonstrates the presence of a second W boson in t (t) over bar candidates in the W(--> l nu) + greater than or equal to 4 jet channel

    First observation of the all-hadronic decay of t(t)over-bar pairs

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    We present the first observation of the all hadronic decay of t (t) over bar pairs. The analysis is performed using 109 pb(-1) of p (p) over bar collisions at root s = 1.8 TeV collected with the Collider Detector at Fermilab. We observe an excess of events with five or more jets, including one or two b jets, relative to background expectations. Based on this excess we evaluate the production cross section to be in agreement with previous results. We measure the top mass to be 186 +/- 10 +/- 12 GeV/c(2)

    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 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 present a measurement of the t (t) over bar production cross section in p (p) over bar collisions at root s = 1.8 TeV using an integrated luminosity of 109 pb(-1) collected with the Collider Detector at Fermilab. The measurement uses t (t) over bar decays into final states which contain one or two high transverse momentum leptons and multiple jets, and final states which contain only jets. Using acceptances appropriate for atop quark mass of 175 GeV/c(2), we find sigma(ii) = 7.6(-1.5)(+1.8) pg

    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

    Measurement of the top quark mass and t(t)over-bar production cross section from dilepton events at the collider detector at Fermilab

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    We present an analysis of dilepton events originating from t(t)over-bar production in p(p)over-bar collisions at root s = 1.8 TeV at the Fermilab Tevatron Collider. The sample corresponds to an integrated luminosity of 109 +/- 7 pb(-1). We observe nine candidate events, with an estimated background of 2.4 +/- 0.5 events. M-top = 161 +/- 17(stat) +/- 10(syst) GeV/c(2). We determine the mass of the top quark to be M-top = 161 +/- 17(stat) +/- 10(syst) GeV/c(2). In addition, we measure a t(t)over-bar production cross section of 8.2(-3.4)(+4.4) pb (where M-top = 175 GeV/c(2) has been assumed for the acceptance estimate)

    Limits on the production of narrow t(t)over-bar resonances in p(p)over-bar collisions at root s=1.96 TeV

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    We search for evidence of resonant top quark pair production in 955 pb(-1) of p (p) over bar collisions at root s = 1: 96 TeV recorded with the CDF II detector at the Fermilab Tevatron. For fully reconstructed candidate t (t) over bar events triggered on leptons with large transverse momentum and containing at least one identified b-quark jet, we compare the invariant mass spectrum of t (t) over bar pairs to the expected superposition of standard model t (t) over bar, non-t (t) over bar backgrounds, and a simple resonance model based on a sequential Z\u27 boson. We establish upper limits for sigma(p (p) over bar -\u3e Z\u27)center dot Br(Z\u27 -\u3e t (t) over bar) in the Z\u27 mass interval from 450 GeV/c(2) to 900 GeV=c(2). A topcolor leptophobic Z\u27 is ruled out below 720 GeV=c(2), and the cross section of any narrow Z\u27-like state decaying to t (t) over bar is found to be less than 0.64 pb at 95% C. L. for M-Z\u27 above 700 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

    Search for anomalous kinematics in t(t)over-bar Dilepton events at CDF II

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    We report on a search for anomalous kinematics of t (t) over bar dilepton events in p (p) over bar collisions at root s = 1: 96 TeV using 193 pb(-1) of data collected with the CDF II detector. We developed a new a priori technique designed to isolate the subset in a data sample revealing the largest deviation from standard model (SM) expectations and to quantify the significance of this departure. In the four-variable space considered, no particular subset shows a significant discrepancy, and we find that the probability of obtaining a data sample less consistent with the SM than what is observed is 1.0%-4.5%
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