Thesis (Ph. D.)--University of Washington, 1998. / Vita. Includes bibliographical references (p. [69]-72).

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (p. 99-116).

Thesis (Ph. D.)--University of Oregon, 2005. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 219-223). Also available for download via the World Wide Web; free to University of Oregon users.

The potential for probing the Standard Model of elementary particle physics by measuring the interactions of W -bosons with Z0-bosons and photons (WW and WWZ triple gauge-boson couplings) using TeV-scale proton-proton collisions is described in the context of the ATLAS detector at the 14 TeV Large Hadron Collider (LHC). The ATLAS detector and LHC are currently under construction at the European Organization for Nuclear Research (CERN), with the rst data expected in 2006. New analysis techniques are presented in this thesis: (1) A new strategy for placing limits on the consistency of measured anomalous triple gauge-boson coupling parameters with the Standard Model is presented. The strategy removes the ambiguities of form factors, by reporting the limits as a function of a cuto operating on the diboson system invariant mass. (2) The `optimal observables' analysis strategy is investigated in the context of hadron colliders, and found to be not competitive, as compared to other strategies. (3) Techniques for measuring the energy dependence of anomalous couplings are presented .. . / Graduate / 0798

An important question at present in particle physics is whether the recently discovered boson with a mass of about 125 GeV is the Standard Model Higgs boson. A Standard Model Higgs boson with a mass of 125 GeV will predominantly decay to b-quark pairs. This work presents the author's contribution to the search with the ATLAS detector for a Standard Model Higgs boson produced in association with a W or Z boson and decaying to b-quark pairs. In order to search for the decay modes ZH → vvb¯b, WH → lvb¯b and ZH → l¯lb¯b, where l is either an electron or muon, events with zero, one or two electrons or muons are considered in 20:3 fb¯1 of 8 TeV LHC data. A Standard Model Higgs boson is not observed decaying to b-quark pairs, although neither is this decay mode ruled out. A Standard Model Higgs boson with a mass of between 110 GeV and 115 GeV is excluded. For mH = 125 GeV the observed (expected) upper limit on the cross- section times the branching ratio is found to be 2.16 (1.07) times the Standard Model prediction. For a Standard Model Higgs boson with a mass of 125 GeV, the best fit signal strength is μ = 1:09 +0:43-0:42 (stat) +0:44-0:37 (syst) = 1:09 +0:61-0:56. The combined results are consistent with a Standard Model Higgs boson with a mass of 125 GeV. The author's own work is presented, including estimation of systematic uncertainties on WH → lvb¯b modelling, and future ATLAS data selection methods for WH → lvb¯b searches. Overviews of underlying theoretical matters and the experimental facilities used are given.

Cette these a pour sujet la recherche de nouvelle physique et l'etude de la production Drell-Yan dans le canal di-electron a l'aide du detecteur CMS au LHC. Certaines theories au dela du Modele Standard (extra dimensions, theories de grande unification) predisent l'existence de particules massives pouvant se desintegrer en une paire d'electrons. La selection des evenements recherches est presentee et etudiee. La strategie d'analyse est introduite et testee. Enfin, l'analyse des premieres donnees a 7 TeV est decrite et les resultats sont commentes.

The Minimal Scale Invariant extension of the Standard Model (MSISM) is a model of low-energy particle physics which is identical to the Standard Model except for the inclusion of an additional complex singlet scalar and tree-level scale invariance. Scale invariance is a classical symmetry which is explicitly broken by quantum corrections whose interplay with the quartic couplings can be used to trigger electroweak symmetry breaking. The scale invariant Standard Model suffers from a number of problems, however the inclusion of a complex singlet scalar results in a perturbative and phenomenologically viable theory. We present a thorough and systematic investigation of the MSISM for a number of representative scenarios along two of its three classified types of flat direction. In these scenarios we determine the permitted quartic coupling parameter space, using both theoretical and experimental constraints, and apply these limits to make predictions of the scalar mass spectrum and the energy scale at which scale invariance is broken. We calculate the one-loop effective potential and the one-loop beta functions of the pertinent couplings of the MSISM specifically for this purpose. We also discuss the phenomenological implications of these scenarios, in particular, whether they realise explicit or spontaneous CP violation, contain neutrino masses or provide dark matter candidates. Of particular importance is the discovery of a new minimal scale invariant model which provides maximal spontaneous CP violation, can naturally incorporate neutrino masses, produces a massive stable scalar dark matter candidate and can remain perturbative up to the Planck scale. It can be argued that the last property, along with the classical scale invariance, can potentially solve the gauge hierarchy problem for this model.

Everything that humans have ever touched, created or built something from consists of a type of matter that only makes up 15 percent of the total matter in the universe. The remaining 85 percent is attributed to dark matter, a so far not discovered and non-luminous type of matter. In this thesis a potential dark matter particle candidate has been studied by investigating an extension of the SU(2) symmetry into a dark gauge sector, where the new sector is connected to the standard model through a vector-like fermion portal. In order to understand how such an extension is made, the Lagrangian density of the standard model and its different gauge sectors were derived. The cross sections of the process of pair production of dark matter particles and tau leptons in the final state due to proton-proton collisions at the LHC was simulated with the software \texttt{MadGraph}. The cross sections were used to draw significance contours for the exclusion and discovery regions for parts of the parameter space of the new model, for current and projected luminosities of the LHC. The projected luminosity scans also consider how lowering the uncertainty in the number of background events through hypothetical improvements to detectors would impact the exclusion and discovery contours. The significance contours were combined with relic density constraints, derived from comparisons between measurements of the Planck telescope and calculations from the software \texttt{MicrOMEGAs}. The resulting graphs show that there are non-forbidden regions of the parameter space that are significant for exclusion and discovery for luminosity of current searches. Increasing the luminosity while keeping the uncertainty in the number of background events the same yielded only minor increases to the exclusion and discovery contours. Combining the projected luminosities with improvements to the background uncertainty instead produced exclusion and discovery regions that were significantly larger than those for the current luminosity.

In the current LHC era, a vast number of models for BSM physics are being tested. For predictions accurate enough to match experimental errors, theoretical calculations have to go beyond LO estimates. However, calculating one-loop corrections in BSM models involves many new particles with specific model dependent properties. Therefore, they are done largely by hand, or in partially–automated ways. I present a fully automated tool for the calculation of generic massive one-loop Feynman diagrams with four external particles, implemented as a module within the fully automated MadGolem framework. With this one can compute the NLO–QCD corrections to generic BSM heavy resonance production processes, for example in the context of supersymmetric theories.

Thesis presented in fulfilment of the requirements for the degree of Master of Science in Physics at the University of the Witwatersrand School of Physics, University of the Witwatersrand, 2015. / A search for the pseudoscalar A boson, which is predicted by in many models with an extended Higgs sector, gives a gateway to searches for physics beyond the Standard Model (SM). This thesis presents the results of a search for gluon-fusion produced A in the decay to Zh, with a final state of two electrons or muons and two τ leptons, in 20.3 fb−1of proton-proton collision data at √s = 8 TeV. Each tau lepton is allowed to dacay either leptonically, τlep, or hadronically,τhad, giving rise to three final states, τlepτlep, τlepτhad and τhadτhad. Focus is placed on the methodology and results of the fully hadronic channel. No evidence for the existence of an A boson is found in the scanned range of 220 ≤ mA ≤ 1000 GeV and 95% CL upper limits are placed on the gluon-fusion cross section times branching ratio, σ × BR(A → Zh) × BR(h → ℓℓττ). The results are combined with a complementing A → Zh search, where h → b¯b, and interpreted in view of two-Higgs-Doublet-Models (2HDMs), where exclusion limits are placed on large sections of phasepace.