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Author: Dmitri Vitalievich Smirnov
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Published: 2005
Total Pages: 358
ISBN-13:
DOWNLOAD EBOOKAuthor: Robert E. Calkins
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Published: 2012
Total Pages: 241
ISBN-13: 9781267906960
DOWNLOAD EBOOKAbstract : In the Standard Model, the top quark plays a unique role as the heaviest known fundamental particle and as a quark that decays before it is able to hadronize. Top quarks are expected to decay to a W-boson and a b-quark nearly 100% of the time. If the branching ratio of t → Wb is lower than one, the distribution of the number of b-tagged jets will shift to lower multiplicities. A simultaneous likelihood fit to the number of b-tagged jets distributions in the lepton+jets and dilepton channels is performed on 4.7 fb−1 of data collected by the ATLAS detector to extract both the branching ratio and the tt ̄ cross section. The branching ratio of t → Wb, R, is measured to be 1.06±0.11, which is consistent with the Standard Model value. This is the first measurement of the t → Wb branching ratio performed with the ATLAS detector using both the lepton+jets and dilepton channels at the LHC. The tt ̄ cross section is measured to be [special characters omitted] pb, which agrees with NNLO predictions.
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Published: 2004
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DOWNLOAD EBOOKUsing 1.0 fb^{-1} of data collected by the Collider Detector at Fermilab (CDF) from Run II of the Fermilab Tevatron, we measure the top-antitop production cross-section in events with two leptons, significant missing transverse energy, and at least jets, at least one of which is identified as a b-jet. As the Run II dataset grows, more stringent tests of Standard Model predictions for the top quark sector are becoming possible. The dilepton channel, where both top quarks decay t-> W b ->l nu b, is of particular interest due to its high purity. Use of an isolated track as the second lepton significantly increases the dilepton acceptance, at the price of some increase in background, particularly from W + jets events where one of the jets is identified as a lepton. To control the increase in background we add to the event selection the requirement that at least one of the jets be identified as a b-jet, reducing the background contribution from all sources. Assuming a branching ratio of BR(W->l nu) = 10.8% and a top mass of m_top = 175 GeV/c^{2} the measured cross-section is sigma = (10.5 +/- 1.8 stat. +/- 0.8 syst. +/- 0.6 lumi.) pb.
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Published: 2015
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DOWNLOAD EBOOKAuthor:
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Published: 2008
Total Pages: 7
ISBN-13:
DOWNLOAD EBOOKThe authors present the first simultaneous measurement of the ratio of branching fractions, R = [Beta](t → Wb)/[Beta](t → Wq), with q being a d, s, or b quark, and the top quark pair production cross section [sigma]{sub t{bar t}} in the lepton plus jets channel using 0.9 fb−1 of p{bar p} collision data at √s = 1.96 TeV collected with the D0 detector. they extract R and [sigma]{sub t{bar t}} by analyzing samples of events with 0, 1 and ≥ 2 identified b jets. They measure R = 0.97{sub -0.08}{sup +0.09} (stat+syst) and [sigma]{sub t{bar t}} = 8.18{sub -0.84}{sup +0.90}(stat+syst) ± 0.50 (lumi) pb, in agreement with the standard model prediction.
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Publisher:
Published: 2005
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DOWNLOAD EBOOKWe present a measurement of the ratio of top-quark branching fractions R = [Beta](t 2!Wb)/[Beta](t 2!Wq) using lepton-plus-jets and dilepton data sets with integrated luminosity of H"62 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{bar t} events with different multiplicity of identified secondary vertices. We set a lower limit of R> 0.61 at 95% confidence level.
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Published: 2008
Total Pages: 7
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DOWNLOAD EBOOKThe authors present the first simultaneous measurement of the ratio of branching fractions, R =?(t → Wb)/?(t → Wq), with q being a d, s, or b quark, and the top quark pair production cross section?{sub t{bar t}} in the lepton plus jets channel using 0.9 fb−1 of p{bar p} collision data at √s = 1.96 TeV collected with the D0 detector. they extract R and?{sub t{bar t}} by analyzing samples of events with 0, 1 and ≥ 2 identified b jets. They measure R = 0.97{sub -0.08}{sup +0.09} (stat+syst) and?{sub t{bar t}} = 8.18{sub -0.84}{sup +0.90}(stat+syst) ± 0.50 (lumi) pb, in agreement with the standard model prediction.
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Published: 1995
Total Pages: 8
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DOWNLOAD EBOOKThe top search in the dilepton and lepton plus jets channels with the Collider Detector at Fermilab is presented. The analysis uses a 67 pb−1 sample of p{bar p} collisions at 1.8 TeV. A 4.8[sigma] excess of candidate events establishes the existence of the top quark. The t{bar t} production cross section is measured to be [sigma]{sub t{bar t}} = 7.6{sub -2.0}{sup +2.4} pb with branching Br(t → Wb) = 0.87{sub -0.30}{sup +0.13}(stat) {sub -0.11}{sup +0.13}(syst). The measured mass is M{sub top} = 176±8±10 GeV.
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Publisher:
Published: 2008
Total Pages: 24
ISBN-13:
DOWNLOAD EBOOKThe authors present a measurement of the mass of the top quark using data corresponding to an integrated luminosity of 1.9 fb−1 of p{bar p} collisions collected at (square root)s = 1.96 TeV with the CDF II detector at Fermilab's Tevatron. This is the first measurement of the top quark mass using top-antitop pair candidate events in the lepton + jets and dilepton decay channels simultaneously. They reconstruct two observables in each channel and use a non-parametric kernel density estimation technique to derive two-dimensional probability density functions from simulated signal and background samples. The observables are the top quark mass and the invariant mass of two jets from the W decay in the lepton + jets channel, and the top quark mass and the scalar sum of transverse energy of the event in the diletpon channel. They perform a simultaneous fit for the top quark mass and the jet energy scale, which is constrained in situ by the hadronic W boson mass. using 332 lepton + jets candidate events and 144 diletpon candidate events, they measure the top quark mass to be m{sub top} = 171.9 ± 1.7 (stat. + JES) ± 1.1 (other sys.) GeV/c2 = 171.9 ± 2.0 GeV/c2.
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Published: 2010
Total Pages: 6
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DOWNLOAD EBOOKSince the discovery of the top quark in 1995 at the Fermliab Tevatron Collider, top quark properties have been measured with ever higher precision. In this article, recent measurements of the top quark mass and its width using up to 3.6 fb−1 of D0 data are summarized. Different techniques and final states have been examined and no deviations within these measurements have been observed. In addition to the direct measurements, a measurement of the top quark mass from its production cross section and a measurement of the top-antitop quark mass difference are discussed. With a mass of 173.3 ± 1.1 GeV, the top quark is the heaviest of all known fundamental particles. Due to the high mass, its Yukawa coupling is close to unity suggesting that it may play a special role in electroweak symmetry breaking. Precise measurements of both, the W boson and the top quark mass, constrain the mass of the yet unobserved Higgs boson and allow to restrict certain extensions of the Standard Model. At the Tevatron collider with a center-of-mass energy of 1.96 TeV, 85% of the top quark pairs are produced in quark-antiquark annihilation; 15% originate from gluon fusion. Top quarks are predicted to decay almost exclusively to a W boson and a bottom quark. According to the number of hadronic W decays, top events are classified into all-jets, lepton+jets and dilepton events. The lepton+jets channel is characterized by four jets, one isolated, energetic charged lepton and missing transverse energy. With 30%, the branching fraction of the lepton+jets channel is about seven times larger than the one of the dilepton channel whereas the signal to background ratio is about three times smaller. The main background in this final state comes from W +jets events. Instrumental background arises from events in which a jet is misidentified as an electron and events with heavy hadrons that decay into leptons which pass the isolation requirements. The topology of the dilepton channel is described by two jets, two isolated, energetic charged leptons and significant missing transverse energy from the undetected neutrinos. The main background are Z + jets and diboson events (WW/WZ/ZZ+jets) as well as instrumental background as characterized above. At the D0 experiment, different techniques are used to measure the top quark mass. They are summarized in the following sections together with the first measurement of the top anti-top quark mass difference and the first precise determination of the top quark width.
