Thesis (M.S.)--University of Texas at El Paso, 2009. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Thesis (Ph. D.)--Carleton University, 1992. / Also available in electronic format on the Internet.

Nous présentons ici, l’analyse détaillée et l’étude de la stabilité de nouvelles solutions de type vortex dans le secteur bosonique de la théorie électrofaible. Les nouvelles solutions généralisent le plongement des solutions d’Abrikosov-Nielsen-Olesen dans la théorie électrofaible et reproduisent les résultats précédemment connus. Les vortex, génériquement porteurs d’un courant électrique, sont constitués d’un coeur massif de bosons chargés Wentouré d’une superposition non-linéaire de champs Z et Higgs. Au loin la solution est purement électromagnétique avec un potentiel de Biot et Savart. Les solutions sont génériques de la théorie et existent en particulier pour les valeurs expérimentales des constantes de couplage. Il est en particulier démontré que le courant dont l’échelle typique est le milliard d’Ampères peut être arbitrairement grand. Dans un second temps la stabilité linéaire des vortex supraconducteurs vis-à-vis des perturbations génériques est considérée. Le spectre de l’opérateur de fluctuations est étudié qualitativement. Lorsque des modes instables sont détectés, ils sont explicitement construits ainsi que leurs relations de dispersion. La plupart des modes instables sont supprimés par une périodisation du vortex. Il subsiste cependant un unique mode instable homogène. On peut espérer qu’un tel mode puisse être supprimé par des effets de courbure si une portionde vortex est refermée afin de former une boucle stabilisée par le courant électrique. / In this dissertation, we analyze in detail the properties of new string-like solutions of the bosonic sector of the electroweak theory. The new solutions are current carrying generalizations of embedded Abrikosov-Nielsen-Olesen vortices. We were also able to reproduce all previously known features of vortices in the electroweak theory. Generically vortices are current carrying. They are made of a compact conducting core of charged Wbosons surrounded by a nonlinear superposition of Z and Higgs field. Faraway from the core, the solution is described by purely electromagnetic Biot and Savart field. Solutions exist for generic parameter values including experimental values of the coupling constants. We show that the current whose typical scale is the billion of Ampères can be arbitrarily large.In the second part the linear stability with respect to generic perturbations is studied. The fluctuation spectrum is qualitatively investigated. When negative modes are detected, they are explicitly constructed and their dispersion relation is determined. Most of the unstable modes can be eliminated by imposing periodic boundary conditions along the vortex. However there remains a unique negative mode which is homogeneous. This mode can probably be eliminated by curvature effects if a small piece of vortex is bent into aloop, stabilized against contraction by the electric current.

xviii, 124 p. : ill. (some col.) / This dissertation discusses three topics on scenarios beyond the Standard Model. Topic one is the effects from a fourth generation of quarks and leptons on electroweak baryogenesis in the early universe. The Standard Model is incapable of electroweak baryogenesis due to an insufficiently strong enough electroweak phase transition (EWPT) as well as insufficient CP violation. We show that the presence of heavy fourth generation fermions solves the first problem but requires additional bosons to be included to stabilize the electroweak vacuum. Introducing supersymmetric partners of the heavy fermions, we find that the EWPT can be made strong enough and new sources of CP violation are present. Topic two relates to the lepton avor problem in supersymmetry. In the Minimal Supersymmetric Standard Model (MSSM), the off-diagonal elements in the slepton mass matrix must be suppressed at the 10-3 level to avoid experimental bounds from lepton avor changing processes. This dissertation shows that an enlarged R-parity can alleviate the lepton avor problem. An analysis of all sensitive parameters was performed in the mass range below 1 TeV, and we find that slepton maximal mixing is possible without violating bounds from the lepton avor changing processes: μ [arrow right] eγ; μ [arrow right] e conversion, and μ [arrow right] 3e. Topic three is the collider phenomenology of quirky dark matter. In this model, quirks are particles that are gauged under the electroweak group, as well as a \dark" color SU (2) group. The hadronization scale of this color group is well below the quirk masses. As a result, the dark color strings never break. Quirk and anti-quirk pairs can be produced at the LHC. Once produced, they immediately form a bound state of high angular momentum. The quirk pair rapidly shed angular momentum by emitting soft radiation before they annihilate into observable signals. This dissertation presents the decay branching ratios of quirkonia where quirks obtain their masses through electroweak symmetry breaking. This dissertation includes previously published and unpublished co-authored material. / Committee in charge: Dr. Davison Soper: Chair; Dr. Graham Kribs: Advisor; Dr. Ray Frey: Member; Dr. Michael Kellman: Outside Member

The discovery of a light scalar at the Large Hadron Collider is in basic agreement with the predictions of an elementary Higgs in the Standard Model (SM). Nonetheless, a light, fundamental scalar is difficult to accommodate in the SM because quantum corrections suggest its mass should be much higher than the scale of electroweak symmetry breaking (EWSB). A natural possibility is to replace the Higgs by a strongly coupled composite. Composite dynamics also gives a natural explanation to the origin of EWSB. Phenomenologically viable composite models of EWSB are constrained by experiment to feature approximate scale invariance. This behavior may follow from near conformal dynamics. At present, lattice gauge theory (LGT) provides the only quantitative method to study near conformal composite Higgs dynamics in a fully consistent strongly coupled relativistic quantum field theory. As a novel approach to the question of finding and studying near conformal theories, I will apply LGT to the study of a generalization of Quantum ChromoDynamics (QCD) with four chiral fermion flavors plus eight flavors of finite, tunable mass. By continuously varying the mass of the eight heavy flavors, I can tune between the four flavor chirally broken theory, which exhibits features similar to QCD, and the twelve flavor theory, which is known to have a conformal fixed point. This is the "4+8 Model" for directly studying near-conformal behavior. In this dissertation, I will review modern composite phenomenology, followed by outlining a study of the 4+8 Model over a range of heavy flavor masses. As a check of near-conformal behavior, I will measure the scale dependent coupling with the method of the Wilson Flow. After verifying the existence of controllable, approximate scale invariance, I will measure the low energy particle spectrum of the 4+8 Model. This includes a Higgs-like light composite scalar. Throughout this dissertation I will make reference to LGT measurement code I wrote and contributed to the software package FUEL.

Title: Dynamical symmetry breaking in models with strong Yukawa in- teractions Author: Petr Beneš Department: Institute of Theoretical Physics, Faculty of Mathematics and Physics, Charles University Supervisor: Ing. Jiří Hošek, DrSc., Department of Theoretical Physics, Nu- clear Physics Institute, Academy of Sciences of the Czech Repub- lic Abstract: The primary aim of the thesis is to explore the possibility of spon- taneous symmetry breaking by strong Yukawa dynamics. Tech- nically, the symmetry is assumed to be broken by formation of symmetry-breaking parts of both the scalar and the fermion prop- agators, rather than by the scalar vacuum expectation values. The idea is first introduced on an example of a toy model with the underlying symmetry being an Abelian one and later applied to a realistic model of electroweak interaction. In addition, the thesis also deals with some more general, model-independent is- sues, applicable not only to the discussed model of strong Yukawa dynamics, but to a wider class of models with dynamical mass generation. First of these issues is the problem of fermion flavor mixing in the presence of fermion self-energies with a general mo- mentum dependence. It is in particular shown how to define the CKM matrix in such models and argued that it can come out in principle...

Cette thèse présente la première investigation expérimentale de la diffusion des bosons massifs (VBS) dans le canal ZZ où les deux bosons de Z se désintégrés en muons où électrons et sont associées avec deux jets hadroniques (ZZjj->lll’l’jj, l=e,mu). VBS constitue un processus clé dans la compréhension de la physique de la brisure de la symétrie électrofaible et le rôle du boson de Higgs découvert en 2012. Cette étude exploite 35.9fb-1 des collisions proton-proton enregistrés avec le détecteur CMS au Grand collisionneur des hadrons (LHC) à sqrt(s) = 13 TeV. Une analyse multivarié (MVA) est utilisée pour séparer le signal électrofaible du bruit de fond irréductible QCD et pour mesurer la force du signal mu, c'est-à-dire le quotient des nombres d'événements observés et celles attendues. La force du signal observé est de mu = 1.39 (+0.86 -65) et exclut l'hypothèse de l'absence d’un signal à 2.7 écart type (1.6 écart type attendue). Des limites sur la physique au-delà du modèle standard sont dérivés sur les couplages quartiques anomaux dans le cadre de la théorie des champs effectifs (EFT), résultant dans les limites les plus rigoureux sur les couplages des opérateurs T8 et T9.L’analyse VBS dans le canal ZZjj demande une modélisations exacte du signal et du bruit de fond irréductible, exigeant des nouveaux simulations. Des efforts intensifs sur la génération et comparaison des prédictions théoriques de plusieurs générateurs d'événements MC est présenté. La compréhension détaillée du signal et des bruit des fonds sont exploités pour développer et optimiser de façon systématique un arbre de décision boosté (BDT). Un classificateur basé sur les éléments de matrices et également développé et sa puissance comparé aux BDT, montrant des performances identiques. La technique d’extraction du signal par un fit des templates de tous les événements permets d’aussi contraindre la normalization du bruit de fond QCD par les données.Des analyses à quatre leptons comme la recherche pour le processus VBS dans le canal ZZ dépend de la capacité de reconstruire et identifier de façon efficace les leptons dans l'état final. Cette thèse présente des optimisations du algorithme multivarié d’identification des électrons utilisé dans les premiers données à 13 TeV en 2015. L'exploitation des variables liées aux traces des électrons permette une réduction de 50% du bruit de fond des électrons non-prompt. En suivant les changements dans la reconstruction des électrons et grâce à une optimisation continue des algorithmes, la performance dans l'identification des électrons a été maintenue pour les donnés enregistrés en 2016 malgré l’empilement plus sévère. La mesure d'efficacité de sélection d'électrons utilisées pour tous les études à multi-leptons dans CMS sont également documenté. / This thesis reports the first experimental investigation into vector boson scattering (VBS) in the the ZZ channel, where both Z bosons are required to decay into electrons or muons and are accompanied by at least two hadronic jets (ZZjj->lll’l’jj, l=e,mu). VBS is a key process in the elucidating the physics of electroweak symmetry breaking and the role of the recently discovered Higgs boson. The study analyses 35.9fb-1 of proton-proton collisions collected with the CMS experiment at the CERN Large Hadron Collider at a center-of-mass energy of 13 TeV. A multivariate analysis (MVA) technique is exploited to separate the electroweak signal from the QCD irreducible background and to measure the signal strength mu, that is the ratio of the observed number of events to the standard model expectation. The observed signal strength is mu = 1.39 (+0.86 -65) which excludes the background-only hypothesis at 2.7 standard deviations (1.6 standard deviations expected). Limits on physics beyond the standard model are derived in terms of anomalous quartic gauge couplings in the effective field theory approach, providing the most stringent constraints to date on the couplings for the operators T8 and T9.The ZZjj VBS analysis requires an accurate modelling of the signal and irreducible background processes, going beyond the existing simulations. Extensive work on generating and comparing the theory predictions from several MC event generators is presented. The detailed understanding of the signal and background kinematics is used to develop and systematically optimize a boosted decision tree (BDT) classifier. A matrix-element discriminant is also developed and its classification performance compared to the BDT, finding comparable performance and indicating that the BDT is adequate. The final signal extraction technique via a template fit of all ZZjj events is designed to simultaneously constrain the normalization of the QCD background using the data.Multi-lepton analyses like the search for VBS in the ZZ channel depend on the ability to efficiently reconstruct and identify the final state leptons. This work presents the optimizations on the multivariate electron identification algorithms used in the first data at 13 TeV in 2015. A study on extending the use of tracking information in the MVA resulted in the reduction of the non-prompt electron background by up to 50%. Monitoring changes to the reconstructed electron objects and continuous optimizations allowed to improve or maintain the performance of the electron MVA ID algorithms, despite the harsher pile-up conditions in the 2016 data. The electron efficiency measurements used by the 2016 multi-lepton analyses in CMS are also documented.

Hadronic collisions at the LHC at CERN probe particle interactions at the highest energy scale of any experiment to date. We present a research program measuring Rjet = &sigmaWBR(W&rarr&mu&nu) / (&sigmaZBR(Z&rarr&mu&mu)) as a function of a number of hadronic variables. The measurements are performed with the ATLAS detector at the LHC, using the 2011 data set, consisting of 4.64 fb-1 of pp collisions at a center of mass energy of 7 TeV. This measurement is a robust way to test the Standard Model and the modeling of perturbative QCD, and is sensitive to a wide variety of possible new physics in events with high jet ET, including some variations of Supersymmetry. By taking the ratio of W/Z production, a large number of systematic uncertainties cancel, including those associated with luminosity, jet energy scale and resolution, and many theoretical uncertainties. The measurement of Rjet is performed as a function of the pT and rapidity of the 1st-4th leading jet, ST, HT, and a number of dijet variables, including invariant mass and angular separations. The measurements are compared with NLO theoretical predictions from Blackhat+Sherpa, as well as using leading order simulations from Alpgen and Sherpa. Over most of the kinematic phase-space, there is good agreement between the data and theoretical predictions. There is a significant deviation for exactly one selected jet above 30 GeV, where Blackhat+Sherpa over-estimates the ratio Rjet by 12%.

The Q_weak Experiment ran for two and a half years at the Thomas Jefferson National Accelerator Facility in pursuit of Q_w^p, the neutral weak analog to the electric charge of the proton. Qweak measured the parity-violating asymmetry in elastic electron-proton scattering at an extreme forward angle (Q² = 0.0249 (GeV/c)² ). From the data gathered via the 1.16 GeV 180 μA longitudinally polarized electron beam scattering off the unpolarized photons in the liquid hydrogen target, a value of Q_w^p (PVES) = 0.0719 ± 0.0045 was determined. The Standard Model has a definite prediction of Q_w^p (SM) = 0.0708 ± 0.0003, consistent with the value determined by Q_weak which sets a limit on possible new physics up to 7.5 TeV. The theory behind the main measurement of the Q_weak Experiment is described in this document, along with the apparatus that made the measurement possible. Understanding the kinematics of the apparatus was a vital component to Qweak 's final measurement. An in-depth explanation of the tracking system responsible for benchmarking the momentum transfer and scattering angle simulations is included. The unblinded analysis of Q_weak's final result is outlined, as are additional physics results related to the N→ ∆ transition. During April 2012, an opportunity was seized to take ancillary data on the inelastic N→ ∆ transition at a different beam energy(877 MeV) than the nominal Q_weak data. This data, combined with the inelastic data taken at nominal beam energy and a previous measurement, determined a constraint on d_∆ , a low energy constant related to hadronic parity violation, of (3.8 ± 14.7)g_π . It also resulted in a measurement of the beam-normal single-spin asymmetry of the N→ ∆ transition of 149 ± 3 (stat) ± 72 (syst) ppm. This document includes both the longitudinal and transverse analysis of the 877 MeV data. / Doctor of Philosophy / The Q_weak Experiment, run at the Thomas Jefferson National Accelerator Facility, measured the weak charge, the weak force analog of the electric charge of the electromagnetic force, of the proton. Unlike the well-know Large Hadron Collider, which operates on the energy-frontier and directly searches for new particles, Q_weak operates by precisely measuring the results of scattering electrons off of protons. This approach is referred to as the precision frontier and is used to test the Standard Model, which has a well-defined prediction for the weak charge of the proton. Deviations from the Standard Model would suggest that there was new physics beyond the Standard Model affecting the results. However, the Q_weak measured weak charge of the proton, Q_w^p (PVES) = 0.0719 ± 0.0045, is in good agreement with the Standard Model predicted value. This provides a new limit, 7.5 TeV, on possible new physics beyond the Standard Model. The theoretical background and apparatus of the Qweak experiment will be explained in this document. A vital component of the final result was understanding the path and energy of the electron as it passed through the apparatus. This was done via simulation but benchmarked by the tracking system. The tracking system will be explained in detail. The final analysis of the Q_weak measurement of the weak charge will also be explained. A secondary result discussed here focuses on data taken using the Q_weak apparatus but at a different beam energy than the nominal Q_weak data. For this data, the electron scatter inelastically off the proton. The lost kinetic energy of the electron causes the proton to be excited into the first resonance state, the ∆, which quickly decays away. This transition grants access to a low energy constant, d_∆, and a measurement linked to the spins of the electrons being polarized perpendicular to the direction of the beam, B_n. The extraction of these values is covered in detail.

The scattering of electroweak gauge bosons is closely connected to the electroweak gauge symmetry and its spontaneous breaking through the Brout-Englert-Higgs mechanism. Since it contains triple and quartic gauge boson vertices, the measurement of this scattering process allows to probe the self-interactions of weak bosons. The contribution of the Higgs boson to the weak boson scattering amplitude ensures unitarity of the scattering matrix. Therefore, the scattering of massive electroweak gauge bosons is sensitive to deviations from the Standard Model prescription of the electroweak interaction and of the properties of the Higgs boson. At the Large Hadron Collider (LHC), the scattering of massive electroweak gauge bosons is accessible through the measurement of purely electroweak production of two jets and two gauge bosons. No such process has been observed before. Being the channel with the least amount of background from QCD-mediated production of the same final state, the most promising channel for the first measurement of a process containing massive electroweak gauge boson scattering is the one with two like-charge W bosons and two jets in the final state. This thesis presents the first measurement of electroweak production of two jets and two identically charged W bosons, which yields the first observation of a process with contributions from quartic gauge interactions of massive electroweak gauge bosons. An overview of the most important issues in Monte Carlo simulation of vector boson scattering processes with current Monte Carlo generators is given in this work. The measurement of the final state of two jets and two leptonically decaying same-charge W bosons is conducted based on proton-proton collision data with a center-of-mass energy of √s = 8 TeV, taken in 2012 with the ATLAS experiment at the LHC. The cross section of electroweak production of two jets and two like-charge W bosons is measured with a significance of 3.6 standard deviations to be σ(W± W±jj−EW[fiducial]) = 1.3 ± 0.4(stat.) ± 0.2(syst.) fb in a fiducial phase space region selected to enhance the contribution from W W scattering. The measurement is compatible with the Standard Model prediction of σ(W±W± jj−EW[fiducial]) = 0.95 ± 0.06 fb. Based on this measurement, limits on anomalous quartic gauge couplings are derived. The effect of anomalous quartic gauge couplings is simulated within the framework of an effective chiral Lagrangian unitarized with the K-matrix method. The limits for the anomalous coupling parameters α4 and α5 are found to be −0.14 < α4 < 0.16 and −0.23 < α5 < 0.24 at 95 % confidence level. Furthermore, the prospects for the measurement of the electroweak production of two same-charge W bosons and two jets within the Standard Model and with additional doubly charged resonances after the upgrade of the ATLAS detector and the LHC are investigated. For a high-luminosity LHC with a center-of-mass energy of √s = 14 TeV, the significance of the measurement with an integrated luminosity of 3000 fb^−1 is estimated to be 18.7 standard deviations. It can be improved by 30 % by extending the inner tracking detector of the atlas experiment up to an absolute pseudorapidity of |η| = 4.0.