Measurement Of The W Boson Helicity Fractions In The Decays Of Top Quark Pairs To Lepton Jets Final States Produced In Pp Collisions At Sqrt S

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The Standard Model And Beyond

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Author : Paul Langacker
language : en
Publisher: CRC Press
Release Date : 2017-06-26

The Standard Model And Beyond written by Paul Langacker and has been published by CRC Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2017-06-26 with Science categories.

This new edition of The Standard Model and Beyond presents an advanced introduction to the physics and formalism of the standard model and other non-abelian gauge theories. It provides a solid background for understanding supersymmetry, string theory, extra dimensions, dynamical symmetry breaking, and cosmology. In addition to updating all of the experimental and phenomenological results from the first edition, it contains a new chapter on collider physics; expanded discussions of Higgs, neutrino, and dark matter physics; and many new problems. The book first reviews calculational techniques in field theory and the status of quantum electrodynamics. It then focuses on global and local symmetries and the construction of non-abelian gauge theories. The structure and tests of quantum chromodynamics, collider physics, the electroweak interactions and theory, and the physics of neutrino mass and mixing are thoroughly explored. The final chapter discusses the motivations for extending the standard model and examines supersymmetry, extended gauge groups, and grand unification. Thoroughly covering gauge field theories, symmetries, and topics beyond the standard model, this text equips readers with the tools to understand the structure and phenomenological consequences of the standard model, to construct extensions, and to perform calculations at tree level. It establishes the necessary background for readers to carry out more advanced research in particle physics. Supplementary materials are provided on the author’s website and a solutions manual is available for qualifying instructors.

Measurement Of The W Boson Helicity Fractions In The Decays Of Top Quark Pairs To Lepton Jets Final States Produced In Pp Collisions At Sqrt S

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Author :
language : en
Publisher:
Release Date : 2016

Measurement Of The W Boson Helicity Fractions In The Decays Of Top Quark Pairs To Lepton Jets Final States Produced In Pp Collisions At Sqrt S written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016 with categories.

The W boson helicity fractions from top quark decays in t-tbar events are measured using data from proton-proton collisions at a centre-of-mass energy of 8 TeV. The data were collected in 2012 with the CMS detector at the LHC, corresponding to an integrated luminosity of 19.8 inverse-femtobarns. Events are reconstructed with either one muon or one electron, along with four jets in the final state, with two of the jets being identified as originating from b quarks. The measured helicity fractions from both channels are combined, yielding F[0] = 0.681 +/- 0.012 (stat) +/- 0.023 (syst), F[L] = 0.323 +/- 0.008 (stat) +/- 0.014 (syst), and F[R] = -0.004 +/- 0.005 (stat) +/- 0.014 (syst) for the longitudinal, left-, and right-handed components of the helicity, respectively. These measurements of the W boson helicity fractions are the most accurate to date and they agree with the predictions from the standard model.

Measurement Of The W Boson Helicity In Events With A Single Reconstructed Top Quark In Pp Collisions At Sqrt S

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Author :
language : en
Publisher:
Release Date : 2015

Measurement Of The W Boson Helicity In Events With A Single Reconstructed Top Quark In Pp Collisions At Sqrt S written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015 with categories.

A measurement of the W boson helicity is presented, where the W boson originates from the decay of a top quark produced in pp collisions. The event selection, optimized for reconstructing a single top quark in the final state, requires exactly one isolated lepton (muon or electron) and exactly two jets, one of which is likely to originate from the hadronization of a bottom quark. The analysis is performed using data recorded at a center-of-mass energy of 8 TeV with the CMS detector at the CERN LHC in 2012. The data sample corresponds to an integrated luminosity of 19.7 fb$^{-1}$. The measured helicity fractions are F$_{L}$ = 0.298 " 0.028 (stat) " 0.032(syst), F$_{0}$ = 0.720 " 0.039 (stat) " 0.037(syst), and F$_{R}$ = -0.018 " 0.019 (stat) " 0.011(syst). These results are used to set limits on the real part of the tWb anomalous couplings, g$_{L}$ and g$_{R}$.

Measurement Of The W Boson Helicity In Top Quark Decays From T Bar T Production In Lepton Jets Events In Pp Collisions At Sqrt S

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Author :
language : en
Publisher:
Release Date : 2013

Measurement Of The W Boson Helicity In Top Quark Decays From T Bar T Production In Lepton Jets Events In Pp Collisions At Sqrt S written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013 with categories.

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.)].

Measurement Of The W Boson Helicity Fractions In Top Anit Top Events At 8 Tev In The Lepton Jets Channel With The Atlas Detector

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Author : Mohammad Jawad Kareem
language : en
Publisher:
Release Date : 2017

Measurement Of The W Boson Helicity Fractions In Top Anit Top Events At 8 Tev In The Lepton Jets Channel With The Atlas Detector written by Mohammad Jawad Kareem and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2017 with categories.

Precise measurements of the properties of the top quark allow for testing the Standard Model (SM) and can be used to constrain new physics models. The top quark is predicted in the SM to decay almost exclusively to a W boson and b-quark. Thus, studying the Wtb vertex structure at high precision and in detail is motivated. This thesis presents a measurement of the W boson helicity fractions in top quark decays with top/anit-top events in the lepton + jets final state using proton-proton collisions at a centre-of-mass energy of 8 TeV recorded in 2012 with the ATLAS detector at the LHC. The da...

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 +}

Search For W To Tb Decays In The Lepton Jets Final State In Pp Collisions At Sqrt S

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Author :
language : en
Publisher:
Release Date : 2014

Search For W To Tb Decays In The Lepton Jets Final State In Pp Collisions At Sqrt S written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2014 with categories.

Results are presented from a search for the production of a heavy gauge boson W' decaying into a top and a bottom quark, using a data set collected by the CMS experiment at sqrt(s) = 8 TeV and corresponding to an integrated luminosity of 19.5 inverse femtobarns. Various models of W'-boson production are studied by allowing for an arbitrary combination of left- and right-handed couplings. The analysis is based on the detection of events with a lepton (e, mu), jets, and missing transverse energy in the final state. No evidence for W'-boson production is found and 95% confidence level upper limits on the production cross section times branching fraction are obtained. For W' bosons with purely right-handed couplings, and for those with left-handed couplings assuming no interference effects, the observed 95% confidence level limit is M(W')> 2.05 TeV. For W' bosons with purely left-handed couplings, including interference effects, the observed 95% confidence level limit is M(W')> 1.84 TeV. The results presented in this paper are the most stringent limits published to date.

Measurement Of The W Boson Helicity Fractions In Top Quark Decays At Cdf

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Author :
language : en
Publisher:
Release Date : 2007

Measurement Of The W Boson Helicity Fractions In Top Quark Decays At Cdf 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 a measurement of the fractions F0 and F+ of longitudinally polarized and right-handed W bosons in top-quark decays using data collected with the CDF II detector. The data set used in the analysis corresponds to an integrated luminosity of approximately 955 pb−1. We select t{bar t} candidate events with one lepton, at least four jets, and missing transverse energy. Our helicity measurement uses 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 momentum in the top-quark rest-frame. The cos[theta]* distribution in the data is determined by full kinematic reconstruction of the t{bar t} candidates. We find F0= 0.59 ± 0.12(stat){sup +0.07}{sub -0.06}(syst) and F+=-0.03 ± 0.06(stat){sup +0.04}{sub -0.03}(syst), which is consistent with the standard model prediction. We set an upper limit on the fraction of right-handed W bosons of F+ ≤ 0.10 at the 95% confidence level.

Measurement Of The Cross Section Of Top Quark Pairs Produced In Association With A Photon In Lepton Jets Events At 8 S

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Author : Nabin Poudyal
language : en
Publisher:
Release Date : 2021

Measurement Of The Cross Section Of Top Quark Pairs Produced In Association With A Photon In Lepton Jets Events At 8 S written by Nabin Poudyal and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2021 with Physics categories.

The inclusive production cross section of top quark pairs in association with a photon is measured in proton-proton collisions at the LHC with 13 TeV energy using the full RunII data collected by CMS in 2016, 2017, and 2018 with a total corresponding integrated luminosity of 137 fb 8́21 . The relative fraction of ttÎđ events normalized to inclusive tt production is measured. The cross section measurement provides important information about the electromagnetic coupling of the standard model top quark and is sensitive to physics beyond the standard model. The analysis is carried out in the in semileptonic decay channel with a well isolated high P T lepton (electron and muon), at least four jets out of which at least one must be b-tagged, and an isolated photon. Photons may be emitted from initial state radiation, top quarks, and decay products of top quarks. A simultaneous likelihood fit of control regions with the signal region is done to constraint the backgrounds and to extract the ttÎđ cross section. The measurement of the ratio of ttÎđ to tt is 0.02055 ℗ł 0.00099 (syst.) ℗ł 0.00099 (stat.) in the e + jets channel, 0.02156 ℗ł 0.00068 (syst.) ℗ł 0.00068 (stat.) in ℗æ + jets channel, and 0.02203 ℗ł 0.00064 (syst.) ℗ł 0.00064 (stat.) in the l + jets channel. The measured inclusive cross section is 3.81 ℗ł 0.15 (syst.) ℗ł 0.10 (stat.) pb in e + jets channel, 3.87 ℗ł 0.11 (syst.) ℗ł 0.07 (stat.) pb in ℗æ + jets channel, and 3.96 ℗ł 0.10 (syst.) ℗ł 0.06 (stat.) pb in l + jets channel for full RunII data. The results are in agreement with the standard model next to leading order prediction.