Measurement Of The W Boson Helicity In Top Quark Decay At

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Measurement Of The W Boson Helicity In Top Quark Decays Using 5 4 Fb Boldsymbol 1 Of Boldsymbol P Bar P Collision Data

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Author :
language : en
Publisher:
Release Date : 2010

Measurement Of The W Boson Helicity In Top Quark Decays Using 5 4 Fb Boldsymbol 1 Of Boldsymbol P Bar P Collision Data written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.

We present a measurement of the helicity of the W boson produced in top quark decays using t{bar t} decays in the l+jets and dilepton final states selected from a sample of 5.4 fb−1 of collisions recorded using the D0 detector at the Fermilab Tevatron p{bar p} collider. We measure the fractions of longitudinal and right-handed W bosons to be f0 = 0.669 ± 0.102 [±0.078 (stat.) ± 0.065 (syst.)] and f+ = 0.023 ± 0.053 [±0.041 (stat.)±0.034 (syst.)], respectively. This result is consistent at the 98% level with the standard model. A measurement with f0 fixed to the value from the standard model yields f+ = 0.010 ± 0.037 [±0.022 (stat.) ± 0.030 (syst.)].

Top Quark Physics At Hadron Colliders

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Author : Arnulf Quadt
language : en
Publisher: Springer Science & Business Media
Release Date : 2007-08-16

Top Quark Physics At Hadron Colliders written by Arnulf Quadt and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2007-08-16 with Science categories.

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.

Measurement Of The W Boson Helicity In Top Quark Decay At

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Author :
language : en
Publisher:
Release Date : 2006

Measurement Of The W Boson Helicity In Top Quark Decay At written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with categories.

The authors present a measurement of the fraction f+ of right-handed W bosons produced in top quark decays, based on a candidate sample of t{bar t} events in the l+jets and dilepton decay channels corresponding to an integrated luminosity of 370 pb−1 collected by the D0 detector at the Fermilab Tevatron p{bar p} Collider at √s = 1.96 TeV. They reconstruct the decay angle [theta]* for each lepton. By comparing the cos[theta]* distribution from the data with those for the expected background and signal for various values of f+, they find f+ = 0.056 ± 0.080(stat) ± 0.057(syst). (f+

Model Independent Measurement Of The W Boson Helicity In Top Quark Decays At

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Author :
language : en
Publisher:
Release Date : 2007

Model Independent Measurement Of The W Boson Helicity In Top Quark Decays At written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2007 with categories.

We present the first model-independent measurement of the helicity of W bosons produced in top quark decays, based on a 1 fb−1 sample of candidate t{bar t} events in the dilepton and lepton plus jets channels collected by the D0 detector at the Fermilab Tevatron p{bar p} Collider. We reconstruct the angle [theta]* between the momenta of the down-type fermion and the top quark in the W boson rest frame for each top quark decay. A fit of the resulting cos [theta]* distribution finds that the fraction of longitudinal W bosons f0 = 0.390 ± 0.177 (stat.) ± 0.104 (syst.) and the fraction of right-handed W bosons f+ = 0.171 ± 0.102 (stat.) ± 0.058 (syst.), which is consistent at the 27% C.L. with the standard model.

Measurement Of The Helicity Of W Bosons In Top Quark Decays

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Author : David J. Winn
language : en
Publisher:
Release Date : 2000

Measurement Of The Helicity Of W Bosons In Top Quark Decays written by David J. Winn and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2000 with categories.

Measurement Of The W Boson Helicity In Top Antitop Quark Events With The Cdf Ii Experiment

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Author : Thorsten Chwalek
language : en
Publisher:
Release Date : 2006

Measurement Of The W Boson Helicity In Top Antitop Quark Events With The Cdf Ii Experiment written by Thorsten Chwalek and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with categories.

In 1995 the top quark was discovered at the Tevatron proton-antiproton collider at Fermilab by the CDF and D0 collaborations [1, 2]. It is the most massive known elementary particle and its mass is currently measured with a precision of about 1.3% [3, 4]. However, the measurements of several other top quark properties are still statistically limited, so the question remains whether the Standard Model of elementary particle physics successfully predicts these properties. This thesis addresses one interesting aspect of top quark decay, the helicity of the produced W boson. Until the start of the Large Hadron Collider (LHC) at CERN, the Tevatron with a center-of-mass energy of {radical}s = 1.96 TeV is the only collider, where top quarks can be produced. In the Standard Model the top quark decays predominantly into a W boson and a b quark, with a branching ratio close to 100%. The V-A structure of the weak interaction of the Standard Model predicts that the W{sup +} bosons from the top quark decay t {yields} W{sup +}b are dominantly either longitudinally polarized or left handed, while right handed W bosons are heavily suppressed and even forbidden in the limit of a massless b quark. Under the assumption of a massless b quark, for a top quark mass of 173 GeV/c{sup 2} the Standard Model predicts the fraction F0 of longitudinally polarized W bosons to be 0.7 and 0.3 for the fraction F{_} of left handed W bosons, while the fraction F{sub +} of right handed W bosons is predicted to be zero. Since next-to-leading order corrections change these fractions only slightly, a significant deviation from the predicted value for F{sub 0} or a nonzero value for F{sub +} could indicate new physics. Left-right symmetric models [5], for example, lead to a significant right handed fraction of W bosons in top decays. Such a right handed component (V+A coupling) would lead to a smaller left handed fraction, while F{sub 0} would remain unchanged. Since the decay rate to longitudinal W bosons depends on the Yukawa coupling of the top quarks, the measurement of F{sub 0} is sensitive to the mechanism of electroweak symmetry breaking. Alternative models can lead to an altered F{sub 0} fraction. In this analysis the W helicity fractions are measured in a selected sample rich in t{bar B} events where one lepton, at least four jets, and missing transverse energy are required. All kinematic quantities describing the t{bar t} decay are determined. As a sensitive observable, we use the cosine of the decay angle {theta}*, which is defined as the angle between the momentum of the charged lepton in the W boson rest frame and the W boson momentum in the top quark rest frame. The data used in this analysis were taken with the Collider Detector at Fermilab (CDF II) in the years 2002-2006 and correspond to an integrated luminosity of about 955 pb{sup -1}. Previous CDF measurements of the W boson helicity fractions in top quark decays used either the square of the invariant mass of the charged lepton and the b quark jet, M{sub {ell}b}{sup 2}, or the lepton p{sub T} distribution as a discriminant. The D0 collaboration used a matrix-element method to extract a value of F{sub 0}; in a second analysis the reconstructed distribution of cos {theta}* was utilized to measure F{sub +}. CDF gives the latest value of F{sub 0} = 0.74{sub -0.34}{sup +0.22}, while D measured F{sub 0} = 0.56 {+-} 0.31. The CDF collaboration also gives the current upper limit of F{sub +}

Measurement Of The Top Quark Mass In The Dilepton Final State Using The Matrix Element Method

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Author : Alexander Grohsjean
language : en
Publisher: Springer Science & Business Media
Release Date : 2010-10-01

Measurement Of The Top Quark Mass In The Dilepton Final State Using The Matrix Element Method written by Alexander Grohsjean and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010-10-01 with Science categories.

The main pacemakers of scienti?c research are curiosity, ingenuity, and a pinch of persistence. Equipped with these characteristics a young researcher will be s- cessful in pushing scienti?c discoveries. And there is still a lot to discover and to understand. In the course of understanding the origin and structure of matter it is now known that all matter is made up of six types of quarks. Each of these carry a different mass. But neither are the particular mass values understood nor is it known why elementary particles carry mass at all. One could perhaps accept some small generic mass value for every quark, but nature has decided differently. Two quarks are extremely light, three more have a somewhat typical mass value, but one quark is extremely massive. It is the top quark, the heaviest quark and even the heaviest elementary particle that we know, carrying a mass as large as the mass of three iron nuclei. Even though there exists no explanation of why different particle types carry certain masses, the internal consistency of the currently best theory—the standard model of particle physics—yields a relation between the masses of the top quark, the so-called W boson, and the yet unobserved Higgs particle. Therefore, when one assumes validity of the model, it is even possible to take precise measurements of the top quark mass to predict the mass of the Higgs (and potentially other yet unobserved) particles.

Measurement Of The W Boson Helicity In Top Quark Decays

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Author :
language : en
Publisher:
Release Date : 2007

Measurement Of The W Boson Helicity In Top Quark Decays written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2007 with categories.

A measurement of the fraction, f+, of right-handed W bosons produced in top quark decays is presented. This analysis is based on a sample corresponding to an integrated luminosity of 370 pb−1, collected by the D0 detector at the Fermilab Tevatron p{bar p} Collider at √s = 1.96 TeV. The helicity angle, [theta]*, is reconstructed for each lepton. f+ is determined by comparing the cos [theta]* distribution from the data with that for the expected background and signal for various values of f+. The fraction of longitudinal W bosons, f°, is assumed to be 0.7 as predicted by the standard model. This yields f+ = 0.109 ± 0.094 (stat) ± 0.063 (syst), consistent with the standard model prediction of f+ = 3.6x 10−4. The possibility that both f+ and f° stray from standard model values is also investigated. In this case cos [theta]* distributions for each possible W helicity state, along with the backgrounds, are fit to the cos [theta]* distribution for the data. The best fit values are f+ = 0.82 ± 0.30(stat) and f° = -0.58 ± 0.50(stat).

Spin Correlations In Tt Events From Pp Collisions

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Author : Boris Lemmer
language : en
Publisher: Springer
Release Date : 2015-06-24

Spin Correlations In Tt Events From Pp Collisions written by Boris Lemmer and has been published by Springer this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015-06-24 with Science categories.

This thesis introduces readers to the Standard Model, the top quark and its properties, before explaining the concept of spin correlation measurement. The first measurement of top quark spin correlations at the LHC in the lepton+jets decay channel is presented. As the heaviest elementary particle, the top quark plays an essential role in the Standard Model of elementary particle physics. In the case of top quarks being produced in pairs at hadron colliders, the Standard Model predicts their spins to be correlated. The degree of correlation depends on both the production mechanism and properties of the top quark. Any deviation from the Standard Model prediction can be an indicator for new physics phenomena. The thesis employs an advanced top quark reconstruction algorithm including dedicated identification of the up- and down-type quarks from the W boson decay.

High Energy Physics

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Author : Hesheng Chen
language : en
Publisher: World Scientific
Release Date : 2005-05-03

High Energy Physics written by Hesheng Chen and has been published by World Scientific this book supported file pdf, txt, epub, kindle and other format this book has been release on 2005-05-03 with Science categories.

The 32nd International Conference on High Energy Physics belongs to the Rochester Conference Series, and is the most important international conference in 2004 on high energy physics. The proceedings provide a comprehensive review on the recent developments in experimental and theoretical particle physics. The latest results on Top, Higgs search, CP violation, neutrino mixing, pentaquarks, heavy quark mesons and baryons, search for new particles and new phenomena, String theory, Extra dimension, Black hole and Lattice calculation are discussed extensively. The topics covered include not only those of main interest to the high energy physics community, but also recent research and future plans. Contents: Neutrino Masses and MixingsQuark Matter and Heavy Ion CollisionsParticle Astrophysics and CosmologyElectroweak PhysicsQCD Hard InteractionsQCD Soft InteractionsComputational Quantum Field TheoryCP Violation, Rare Kaon Decay and CKMR&D for Future Accelerator and DetectorHadron Spectroscopy and ExoticsHeavy Quark Mesons and BaryonsBeyond the Standard ModelString Theory Readership: Experimental and theoretical physicists and graduate students in the fields of particle physics, nuclear physics, astrophysics and cosmology.Keywords:High Energy Physics;Particle Physics;Electroweak;QCD;Heavy Quark;Neutrino;Particle Astrophysics;Hadron Spectroscopy;CP Violation;Quark Matter;Future Accelerator