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Languages : en
Pages : 10
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The observation of the top quark by the D0 experiment, at Fermilab's Tevatron proton-antiproton collider, is briefly reviewed. The analysis of the top quark mass in the lepton plus jets decay channels, resulting in m{sub t} (almost equal to) 200 GeV/c2 is reviewed; and a preliminary mass analysis from the dilepton decay channels resulting in m{sub t} = 145 " 25 (statistical) " 20 (systematic) GeV/c2 is presented. These mass measurements are compared with Standard Model limits from CERN's LEP experiments and the published CDF measurement. Preliminary observation of top quark-W boson correlation is shown.
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Category :
Languages : en
Pages : 10
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Book Description
The observation of the top quark by the D0 experiment, at Fermilab's Tevatron proton-antiproton collider, is briefly reviewed. The analysis of the top quark mass in the lepton plus jets decay channels, resulting in m{sub t} (almost equal to) 200 GeV/c2 is reviewed; and a preliminary mass analysis from the dilepton decay channels resulting in m{sub t} = 145 " 25 (statistical) " 20 (systematic) GeV/c2 is presented. These mass measurements are compared with Standard Model limits from CERN's LEP experiments and the published CDF measurement. Preliminary observation of top quark-W boson correlation is shown.
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Languages : en
Pages : 5
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We present an overview of selected top quark properties in lepton + jets and dilepton final states based on 1-4.3 fb−1 of data, collected with the D0 experiment at the Fermilab Tevatron collider. The recent measurement of theW boson helicity, a search for anomalous top quark couplings, and measurements of spin correlations and forward backward color charge asymmetry are discussed. Since the discovery of top quark in 1995 by CDF and D0, the discovered particle is considered as a standard model (SM) top quark, mainly because its cross-section is in a reasonable agreement with QCD calculations and its measured mass is in a agreement with indirect top quark mass determinations. However the limited precision of these comparisons doesn't exclude the possibility of non SM contributions in the top quark final states, so direct measurements of top quark properties are useful to confirm its SM nature. In this article we report several recent measurements done using 1-4.3 fb−1 of data collected with the D0 detector at the Fermilab Tevatron collider.
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Languages : en
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Author: Dag Gillberg
Publisher: Springer Science & Business Media
ISBN: 1441977996
Category : Science
Languages : en
Pages : 149
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Book Description
The top quark is by far the heaviest known fundamental particle with a mass nearing that of a gold atom. Because of this strikingly high mass, the top quark has several unique properties and might play an important role in electroweak symmetry breaking—the mechanism that gives all elementary particles mass. Creating top quarks requires access to very high energy collisions, and at present only the Tevatron collider at Fermilab is capable of reaching these energies. Until now, top quarks have only been observed produced in pairs via the strong interaction. At hadron colliders, it should also be possible to produce single top quarks via the electroweak interaction. Studies of single top quark production provide opportunities to measure the top quark spin, how top quarks mix with other quarks, and to look for new physics beyond the standard model. Because of these interesting properties, scientists have been looking for single top quarks for more than 15 years. This thesis presents the first discovery of single top quark production. It documents one of the flagship measurements of the D0 experiment, a collaboration of more than 600 physicists from around the world. It describes first observation of a physical process known as “single top quark production”, which had been sought for more than 10 years before its eventual discovery in 2009. Further, his thesis describes, in detail, the innovative approach Dr. Gillberg took to this analysis. Through the use of Boosted Decision Trees, a machine-learning technique, he observed the tiny single top signal within an otherwise overwhelming background. This Doctoral Thesis has been accepted by Simon Fraser University, Burnaby, BC, Canada.
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Languages : en
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The mass of the top quark is a fundamental parameter of the standard model (SM) and has to be determined experimentally. In this talk, I present the most recent measurements of the top quark mass in $p\bar p$ collisions at $\sqrt s=1.96$~TeV recorded by the D0 experiment at the Fermilab Tevatron Collider. The measurements are performed in final states containing two leptons, using 5.4~\fb of integrated luminosity, and one lepton, using 9.7~\fb of integrated luminosity. The latter constitutes the most precise single measurement of the mass of the top quark, corresponding to a relative precision of 0.43\%. I conclude with a combination of our results with the results by the CDF collaboration, attaining a relative precision of 0.37\%.
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Languages : en
Pages : 20
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We present a measurement of the t{anti t} production cross section in p{anti p} collisions at √s = 1.8 TeV and a measurement of top quark mass m{sub t} by the D0 experiment at the Fermilab Tevatron. The measurements are based on the data from the 1992- 1996 run during which the D0 detector was exposed to the integrated luminosity of approximately 125 pb−1. We observe 39 t{anti t} candidate events in the dilepton and lepton+jets decay channels with an expected background of 13.7 ± 2.2 events. We measure the top quark mass m{sub t} using a two constraint fit to m{sub t} in t{anti t} → bW {anti b}W− final states with one W decaying to q{anti q} and the other to e? or??. Events are binned in the fit mass versus a measure of probability for events to be the signal rather than a background. Likelihood fits to the data yield m{sub t} = 173.3 ± 5.6 (stat) ± 6.2 (syst) GeV/c2. For this mass we measure the t{anti t} production cross section to be 5.5 ± 1.8 pb.
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Languages : en
Pages : 7
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The top quark discovery in 1995 at Fermilab is one of the major proofs of the standard model (SM). Due to its unique place in SM, the top quark is an important particle for testing the theory and probing for new physics. This article presents most recent measurements of top quark properties from the D0 detector. In particular, the measurement of the top quark mass, the top antitop mass difference and the top quark decay width. The discovery of the top quark in 1995 confirmed the existence of a third generation of quarks predicted in the standard model (SM). Being the heaviest elementary particle known, the top quark appears to become an important particle in our understanding of the standard model and physics beyond it. Because of its large mass the top quark has a very short lifetime, much shorter than the hadronization time. The predicted lifetime is only 3.3 · 10−25s. Top quark is the only quark whose properties can be studied in isolation. A Lorentz-invariant local Quantum Field Theory, the standard model is expected to conserve CP. Due to its unique properties, the top quark provides a perfect test of CPT invariance in the standard model. An ability to look at the quark before being hadronized allows to measure directly mass of the top quark and its antiquark. An observation of a mass difference between particle and antiparticle would indicate violation of CPT invariance. Top quark through its radiative loop correction to the W mass constrains the mass of the Higgs boson. A precise measurement of the top quark mass provides useful information to the search of Higgs boson by constraining its region of possible masses. Another interesting aspect is that the top quark's Yukawa coupling to the Higgs boson is very close to unity (0.996 ± 0.006). That implies it may play a special role in the electroweak symmetry breaking mechanism.
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Languages : en
Pages : 9
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In these proceedings, I review recent measurements in the top quark sector in pp-bar collisions at a centre-of-mass energy of √s = 1.96 TeV in Run II of the Fermilab Tevatron Collider using the D0 detector. I will present the differential measurement of the tt-bar production cross section and the Tevatron combination of inclusive tt-bar cross section measurements; the first evidence of the production of single top quarks in the s-channel by D0 and the observation in combination with CDF. Furthermore, I will review the measurements of the forward-backward asymmetry in tt-bar events, and conclude with the world's most precise single measurement of the top quark mass, which is a fundamental parameter of the standard model, and present the Tevatron combination, which is the world's most precise determination of the top quark mass, with a relative precision of 0.37%.
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Languages : en
Pages : 7
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We report preliminary results of a search for the top quark by the D{O} collaboration at the Fermilab Tevatron p{bar p} collider using a data sample corresponding to an integrated luminosity of about 7.5 pb−1. Events with a high p{sub T} isolated electron and large missing E{sub T} which are candidates for containing W bosons were studied. Only one vent was found having an additional isolated lepton. Combining the ee and e[mu] channels we set a lower limit of 99 GeV/c2 for the top quark mass.
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Languages : en
Pages : 6
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Book Description
Different measurements of the properties of the top quark using up to 5.4 fb−1 collected with the D0 detector at the Fermilab Tevatron collider are presented. The top mass is obtained from a study of dilepton and lepton+jets final states, while the width is obtained from a combination of the measurements of the single top production via t-channel exchange and the determination of the t → Wb branching ratio. Furthermore the measurement of the helicity of the W boson from top quark decays, a measurement of t{bar t} spin correlations and a measurement of the jet pull (color flow) in t{bar t} events are presented. A wealth of measurements of properties of the top quark at D0 have been discussed showing the great performance of the Tevatron and the D0 detector. All results are consistent with the standard model expectations. The final D0 data sample will have 2-3 times the presented statistics allowing for new & more precise results in the future.
