Top Quark Production at Electron-positron Colliders PDF Download

Author: L.M. Jones
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Category :
Languages : en
Pages :

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Author: Arnulf Quadt
Publisher: Springer Science & Business Media
ISBN: 3540710604
Category : Science
Languages : en
Pages : 166

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This will be a required acquisition text for academic libraries. More than ten years after its discovery, still relatively little is known about the top quark, the heaviest known elementary particle. This extensive survey summarizes and reviews top-quark physics based on the precision measurements at the Fermilab Tevatron Collider, as well as examining in detail the sensitivity of these experiments to new physics. Finally, the author provides an overview of top quark physics at the Large Hadron Collider.

Author: F. Gournaris
Publisher:
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Category :
Languages : en
Pages :

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One of the most important physics targets for any future electron positron linear collider will be the precision measurements of the top quark properties, and especially the top quark mass. Top-antitop production at threshold provides the ideal environment for making such measurements but is complicated by the machine's luminosity spectrum and thus needs to be carefully studied to understand the constraints involved and the potential precision reach. This thesis presents developments in both the understanding of the luminosity spectrum and the top quark production threshold by the means of new simulation tools and simulation results of systematic and statistical uncertainties in the measurements of the luminosity spectrum and the top quark parameters by the use of a threshold scan. The luminosity spectrum is studied by employing a new parametrization method that takes into account the beam energy spread in the fit parameters, and detailed simulation studies of the measurement of the luminosity spectrum by the use of Bhabha scattering events. A detailed account is given of the possible systematic uncertainties arising due to beam-beam and detector induced effects influencing the luminosity measurement, by looking at the different luminosity spectra of the International Linear Collider (ILC) Reference Design Report (RDR) accelerator parameter plane. A new simulation tool for the top quark production threshold is presented, in the form of a new fully differential Monte Carlo event generator using a state-of-the-art next-to-next-to leading order (NNLO) QCD calculation of the top quark production threshold in order to describe the total and differential distributions that can be used in the top threshold measurements, by including a full description of the luminosity spectrum. Finally, a study of how the uncertainties of the luminosity spectrum measurement can affect the top quark threshold measurements is presented, by examining simulated threshold scan measurements for the different luminosity spectra of the ILC RDR accelerator parameter plane.

Author:
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ISBN:
Category :
Languages : en
Pages : 254

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In 1995 the last missing member of the known families of quarks, the top quark, was discovered by the CDF and D0 experiments at the Tevatron, a proton-antiproton collider at Fermilab near Chicago. Until today, the Tevatron is the only place where top quarks can be produced. The determination of top quark production and properties is crucial to understand the Standard Model of particle physics and beyond. The most striking property of the top quark is its mass--of the order of the mass of a gold atom and close to the electroweak scale--making the top quark not only interesting in itself but also as a window to new physics. Due to the high mass, much higher than of any other known fermion, it is expected that the top quark plays an important role in electroweak symmetry breaking, which is the most prominent candidate to explain the mass of particles. In the Standard Model, electroweak symmetry breaking is induced by one Higgs field, producing one additional physical particle, the Higgs boson. Although various searches have been performed, for example at the Large Electron Positron Collider (LEP), no evidence for the Higgs boson could yet be found in any experiment. At the Tevatron, multiple searches for the last missing particle of the Standard Model are ongoing with ever higher statistics and improved analysis techniques. The exclusion or verification of the Higgs boson can only be achieved by combining many techniques and many final states and production mechanisms. As part of this thesis, the search for Higgs bosons produced in association with a top quark pair (t{bar t}H) has been performed. This channel is especially interesting for the understanding of the coupling between Higgs and the top quark. Even though the Standard Model Higgs boson is an attractive candidate, there is no reason to believe that the electroweak symmetry breaking is induced by only one Higgs field. In many models more than one Higgs boson are expected to exist, opening even more channels to search for charged or neutral Higgs bosons. Depending on its mass, the charged Higgs boson is expected to decay either into top quarks or be the decay product of a top quark. For masses below the top quark mass, the top decay into a charged Higgs boson and a b quark can occur at a certain rate, additionally to the decays into W bosons and a b quark. The different decays of W and charged Higgs bosons can lead to deviations of the observed final number of events in certain final states with respect to the Standard Model expectation. A global search for charged Higgs bosons in top quark pair events is presented in this thesis, resulting in the most stringent limits to-date. Besides the decay of top quarks into charged Higgs or W bosons, new physics can also show up in the quark part of the decay. While in the Standard Model the top quark decays with a rate of about 100% into a W boson and a b quark, there are models where the top quark can decay into a W boson and a non-b quark. The ratio of branching fractions in which the top quark decays into a b quark over the branching fractions in which the top quark decays into all quarks is measured as part of this thesis, yielding the most precise measurement today. Furthermore, the Standard Model top quark pair production cross section is essential to be known precisely since the top quark pair production is the main background for t{bar t}H production and many other Higgs and beyond the Standard Model searches. However, not only the search or the test of the Standard Model itself make the precise measurement of the top quark pair production cross section interesting. As the cross section is calculated with high accuracy in perturbative QCD, a comparison of the measurement to the theory expectation yields the possibility to extract the top quark mass from the cross section measurement. Although many dedicated techniques exist to measure the top quark mass, the extraction from the cross section represents an important complementary measurement. The latter is briefly discussed in this thesis and compared to direct top mass measurements. The goal of this thesis is the improved understanding of the top quark sector and its use as a window to new physics. Techniques are extended and developed to measure the top quark pair production cross section simultaneously with the ratio of branching fractions, the t{bar t}H cross section or the rate with which top quarks decay into charged Higgs bosons. Some of the results are then taken to extract more information. The cross section measurement is used to extract the top quark mass, and the ratio of the top quark pair production cross sections in different final states, yielding a limit on non-Standard Model top quark decays.

Author: Dag Gillberg
Publisher: Springer Science & Business Media
ISBN: 1441977996
Category : Science
Languages : en
Pages : 149

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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.

Author: Dan Green
Publisher: Cambridge University Press
ISBN: 9780521835091
Category : Science
Languages : en
Pages : 280

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Author:
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ISBN:
Category :
Languages : en
Pages : 602

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The XXIII SLAC Summer Institute on Particle Physics addressed the physics of the recently discovered top quark, and its connection to the electroweak interaction and to physics beyond the Standard Model. The seven-day school portion of the Institute covered many avenues for studying the top quark, from its direct production at hadron colliders and at future electron-positron colliders, to its virtual effects in precision electroweak quantities, in heavy flavor physics, and in the renormalization of supersymmetric theories, Vertex detectors - critical for identifying the b quark decay products of the top - and Cherenkov techniques for particle identification were also reviewed. The Institute concluded with a three-day topical conference covering recent developments in theory and experiment; this year, the highlights were the CDF and D0 top quark discovery. Also featured were updated precision electroweak measurements from SLC, LEP, and the Tevatron, heavy quark results from these facilities as well as CLEO, and new photoproduction and deep-inelastic scattering data from HERA. Separate abstracts have been submitted to the energy database for articles from this proceedings.

Author: Doulgas Olaf Carlson
Publisher:
ISBN:
Category : Hadron interactions
Languages : en
Pages : 282

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Author: Teresa Rodrigo
Publisher: World Scientific
ISBN: 9814548847
Category :
Languages : en
Pages : 340

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This meeting discussed the experimental results and theoretical aspects in the field of high energy physics, with special reference to the top quark observation, heavy flavor physics and symmetry-breaking mechanisms. The major topics are developed in a series of course lectures.

Author: Stefan Roth
Publisher: Springer Science & Business Media
ISBN: 3540351647
Category : Science
Languages : en
Pages : 182

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This up-to-date volume reviews the recent contributions of electron-positron colliders to the precision test of the electroweak Standard Model. In particular, it contains a short summary of the measurements at the Z resonance and gives an overview of the electroweak processes above the Z. Subsequently, the measurement of the W mass at LEP is discussed in detail. The implications for the precision test of the Standard Model are presented, giving the status of the global electroweak fit before the startup of Large Hadron Collider. The final chapters give an outlook on the electroweak physics at a future linear collider. The book also features many illustrations and tables. Readers obtain a coherent overview of the results of 20 years of electroweak physics conducted at electron-positron colliders.