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Author: Publisher: ISBN: Category : Languages : en Pages : 24
Book Description
The production of the heavy (c{bar c})-quarkonium, (c{bar b})-quarkonium, and (b{bar b})-quarkonium states [({bar Q}') quarkonium for short], via the W semi-inclusive decays, has been systematically studied within the framework of the nonrelativistic QCD. In addition to the two color-singlet S-wave states, we also discuss the production of the four color-singlet P-wave states.
Author: Publisher: ISBN: Category : Languages : en Pages : 24
Book Description
The production of the heavy (c{bar c})-quarkonium, (c{bar b})-quarkonium, and (b{bar b})-quarkonium states [({bar Q}') quarkonium for short], via the W semi-inclusive decays, has been systematically studied within the framework of the nonrelativistic QCD. In addition to the two color-singlet S-wave states, we also discuss the production of the four color-singlet P-wave states.
Author: Valentin Knünz Publisher: Springer ISBN: 3319499351 Category : Science Languages : en Pages : 179
Book Description
This thesis discusses in detail the measurement of the polarizations of all S-wave vector quarkonium states in LHC proton-proton collisions with the CMS detector. Heavy quarkonium states constitute an ideal laboratory to study non-perturbative effects of quantum chromodynamics and to understand how quarks bind into hadrons. The experimental results are interpreted through an original phenomenological approach, which leads to a coherent picture of quarkonium production cross sections and polarizations within a simple model, dominated by one single color-octet production mechanism. These findings provide new insights into the dynamics of heavy quarkonium production at the LHC, an important step towards a satisfactory understanding of hadron formation within the standard model of particle physics.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
In this study, a search is presented for pair production of a new heavy quark (Q) that decays into a W boson and a light quark (q) in the final state where one W boson decays leptonically (to an electron or muon plus a neutrino) and the other W boson decays hadronically. The analysis is performed using an integrated luminosity of 20.3 fb–1 of pp collisions at √s = 8 TeV collected by the ATLAS detector at the LHC. No evidence of QQ¯ production is observed. New chiral quarks with masses below 690 GeV are excluded at 95% confidence level, assuming BR(Q → Wq)=1. Results are also interpreted in the context of vectorlike quark models, resulting in the limits on the mass of a vectorlike quark in the two-dimensional plane of BR(Q → Wq) versus BR(Q → Hq).
Author: Thorsten Chwalek Publisher: ISBN: Category : Languages : en Pages : 102
Book Description
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 +}
Author: Hua-Sheng Shao Publisher: Springer ISBN: 9811016240 Category : Science Languages : en Pages : 173
Book Description
This book focuses on the study of heavy quarkonium production at high-energy colliders as a useful tool to explain both the perturbative and non-perturbative aspects of quantum choromodynamics. It provides the first comprehensive comparison between the theory and recent experiments and clarifies some longstanding puzzles in the heavy quarkonium production mechanism. In addition, it describes in detail a new framework for implementing precise computations of the physical observables in quantum field theories based on recently developed techniques. It can be used to simulate the complicated collider environment of the Large Hadron Collider at the Conseil Européen pour la Recherche Nucléaire (CERN). Its accomplishment implies that the Monte Carlo simulations for high-energy physics experiments have reached the limits of precision. It offers readers a wealth of valuable information on the relevant techniques.
Author: Kuan-Yu Lin Publisher: ISBN: Category : Electronic dissertations Languages : en Pages : 181
Book Description
With the LHC proton-proton collision data at an energy of 13 TeV recorded by the ATLAS detector, this analysis searches for the production of a new particle W' with a yet-to-be-probed mass in the top quark plus bottom quark decay channel. The boosted and hadronically decaying top-quark is reconstructed as a large-radius jet and identified using jet substructures. A secondary-vertex finding algorithm identifies small-radius jets originating from a bottom quark. After the identification stage, the main background events come from the Quantum Chromodynamical production of multi-jet, which is estimated by a data-driven approach. The statistical data analysis searches for a resonant peak in the invariant mass distribution of the system with a jet associated with the top quark and another with the bottom quark. The consistency between data and the background prediction is found in the invariant mass range between 1 TeV to 7 TeV, and an upper limit at the 95% confidence level is set on the production cross-section times branching ratio for a W' boson with right-handed chirality decaying to a top quark and a bottom quark. A lower limit on the W' mass is set at 4.4 TeV accordingly.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
A search is presented for a heavy vector-like quark, decaying into a b quark and a W boson, which is produced singly in association with a light flavor quark and a b quark. The analysis is performed using a data sample of proton-proton collisions at a center-of-mass energy of $\sqrt{s} = $ 13 TeV collected at the LHC in 2015. The data set used in the analysis corresponds to an integrated luminosity of 2.3 inverse-femtobarns. The search is carried out using events containing one electron or muon, at least one b-tagged jet with large transverse momentum, at least one jet in the forward region of the detector, and missing transverse momentum. No excess over the standard model prediction is observed. Upper limits are placed on the production cross section of heavy exotic quarks: a T quark with a charge of 2/3, and a Y quark with a charge of -4/3. For Y quarks with coupling of 0.5 and B(Y to bW) = 100%, the observed (expected) lower mass limits are 1.40 (1.0) TeV. This is the most stringent limit to date on the single production of the Y vector-like quark.
Author: Publisher: ISBN: Category : Languages : en Pages : 9
Book Description
We present a search for the production of a new heavy gauge boson W' that decays to a top quark and a bottom quark. We have analyzed 230 pb−1 of data collected with the D0 detector at the Fermilab Tevatron collider at a center-of-mass energy of 1.96 TeV. No significant excess of events is found in any region of the final state invariant mass distribution. We set upper limits on the production cross section of W bosons at the 95% confidence level for several different W' boson masses. We exclude masses below 610 GeV for a W' boson with standard-model-like couplings, below 630 GeV for a W' boson with right-handed couplings that is allowed to decay to both leptons and quarks, and below 670 GeV for a W' boson with right-handed couplings that is only allowed to decay to quarks.
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Author: Valentin Knünz
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Author: Thorsten Chwalek
Author: Hua-Sheng Shao
Author: Clemens Mellein
Author: Kuan-Yu Lin
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