O Modelo Padrão das partículas elementares descreve com sucesso as interações eletrofracas e fortes da natureza, quando comparado com todos os dados experimentais que temos ate hoje. Porém, ele apresenta problemas relacionados a origem da quebra da simetria eletrofraca assim como da hierarquia das massas dos fermions. A solução de ambos esses problemas requer a geração de grandes hierarquias estáveis. Essas hierarquias podem ser obtidas em uma classe de teorias quadridimensionais chamadas de teorias quiver de hierarquia completa, que são relacionadas a teorias de dimensões extras em AdS no limite de grande número de sítios. Mostramos que, assim como em teorias de dimensões extras curvas, existe um grau de liberdade leve associado com a quebra da invariância de escala, que pode ser identicado com um dílaton. Partindo da teoria extra-dimensional em um fundo, mostramos como esse dílaton leve também pode ser obtido em teorias quiver de hierarquia completa. / The standard model of particle physics successfuly describes the electroweak and strong interactions when compared with all the experimental data we have until now. However, it has problems regarding the origin of electroweak symmetry breaking as well as the hierarchy of fermion masses. The solutions of both these problems require the generation of large stable hierarchies. These can be obtained in a class of four-dimensional quiver theories called full-hierarchy quiver theories, which are related to extra dimensional theories in AdS, in the large-number-ofsites limit. We show that, just as in curved extra dimensional theories, there is a light degree of freedom associated with the breaking of scale invariance, which can be identied with a dilaton. Starting from an extra dimensional theory in an AdS5 background, we show how this light dilaton can be obtained in full-hierarchy quiver theories as well.

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The Qweak experiment has precisely determined the weak charge of the proton Qp w by measuring the parity-violating asymmetry in elastic electron-proton scattering at a low momentum transfer of Q2 = 0.0249 (GeV/c)2 . Qpw has a definite prediction in the Standard Model, and a value of sin2 θW can be extracted from it for comparison with other neutral current observables. Qweak measured the weak charge of the proton to be Qpw(P V ES) = 0.0719 ± 0.0045, which is consistent with the Standard Model value of Qp w(SM) = 0.0708 ± 0.0003. Qweak ran at the Thomas Jefferson National Accelerator Facility for two and a half years and was installed in experimental Hall C. A 180µA beam of longitudinally polarized electrons at 1.16 GeV scattered off a liquid hydrogen target of unpolarized protons. The electrons were collimated to an acceptance of 5.8◦ to 11.6◦ and then passed through a magnetic spectrometer and onto quartz Čerenkov detector bars. A detailed description of the theory and motivation behind the Qweak experiment is given. An overview of the Qweak apparatus and an in-depth discussion of the luminosity monitor performance is presented. A general overview of the Qweak analysis is also presented, with a focus on the beamline background correction, the nonlinearity measurement, and the simulation to constrain error for a rescattering effect. Also detailed here is the final, unblinded Qweak result, which determined Qpw to 6.2% and provided the highest precision measurement of sin2θW at low energy. / PHD

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.

The Standard Model scalar potential contains a minimum at the Electroweak scale, responsible for the masses of the weak gauge bosons through the Higgs mechanism. However, if the Electroweak minimum is only a local minimum, and there exists a global minimum at a higher energy in the Higgs potential, then in a su ciently old universe we would expect the vacuum expectation value to be at the global minimum. The absence of a global minimum at higher energy is related to the condition that the Higgs self coupling is greater than or equal to zero for all energies. For any model that fails this, we expect new physics to enter before the energy at which the coupling becomes negative. We developed tools to automate the derivation of beta functions for renormalisable gauge theories, and used these to carry out evolution of the renormalisation group equations for the Standard Model and three extensions to the Standard Model | the Standard Model with a fourth generation, the Standard Model with right-handed neutrinos and a Left-Right Symmetric Model. We conclude that of these four models, the Standard Model is the only one in which all the couplings remain perturbative, and in which the Electroweak minimum is a global minimum.

In this paper the higgs mechanism for the standard model is constructed in steps. First by considering spontaneous breaking of discrete and continuous global gauge invariance. Then spontaneous breaking of local gauge invariance. These results are then used to construct the electroweak part of the standard model through application of the higgs mechanism. Finally, the LQT-upper bound of 1 TeV for the higgs mass is calculated through unitarity constraints. / I denna artikel konstrueras higgsmekanismen i standardmodellen stegvis. Först genom att beakta spontant symmetribrott av diskreta samt kontinuerliga globala gaugeinvarianser. Därefter spontant symmetribrott av lokala gaugeinvarianser. Dessa resultat används sedan för att konstruera den elektrosvaga delen av standardmodellen genom tillämpning av higgsmekanismen. Slutligen beräknas en övre gräns för higgsmassan, den så kallade LQT-gränsen, via unitaritetsbegränsingar.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Este trabalho apresenta um estudo sobre o espalhamento W+W+ e W&#8722;W&#8722; para os primeiros anos de tomada de dados do experimento CMS do LHC, no CERN. O processo de espalhamento de bósons vetoriais, dentre os quais se inclui o espalhamento WW, é um processo chave para elucidação do mecanismo de quebra de simetria eletrofraca. Previsões teóricas mostram que as características cinemáticas do espalhamento de bósons vetoriais na escala T e V de energia devem depender significativamente do mecanismo que quebra a simetria eletrofraca. Este processo será analisado com dois objetivos principais: estudar a viabilidade de medi-lo em altas energias no CMS, e mostrar a sua sensibilidade ao mecanismo da quebra de simetria eletrofraca. Esta sensibilidade será mostrada através da análise de duas amostras de eventos correspondentes a dois cenários distintos: o modelo padrão com a presença de um bóson de Higgs de massa 500 GeV e o modelo padrão sem a presença do bóson de Higgs. Estas amostras foram geradas com o gerador de eventos PHASE, cuja principal importância para o estudo do espalhamento de bósons vetoriais em altas energias e a sua capacidade de calcular o elemento de matriz completo em ordem dominante O(&#945;6). Para se analisar a viabilidade de se medir o espalhamento WW no CMS, foi feita uma simulação do detector utilizando as amostras dos processos de sinal e dos principais processos de fundo através do pacote de simulação rápida do CMS, o FAMOS. Os processos de fundo, WW+N jatos, WZ+N jatos, ZZ+N jatos, W+N jatos e tt+N jatos, foram estudados e suprimidos através de seleções de regiões cinemáticas. A análise dos dados mostra que a observação do espalhamento WW na fase inicial do LHC será muito difícil, sendo necessária uma luminosidade maior, além de aprimoramento da análise. / This work presents a study of W+W+ and W&#8722;W&#8722; scattering for the first years of the CMS experiment data-taking at LHC, CERN. Vector boson scattering, including WW, is a key processes for probing electroweak symmetry breaking. Theoretical predictions show that kinematics characteristics of vector boson scattering at T e V scale must strongly depend on the electroweak symmetry breaking mechanism. This process is analyzed with two main objectives: viability study of performing this measurement at CMS and show its dependence on the electroweak symmetry breaking mechanism. This dependence is shown through an analysis with two event samples corresponding to two distinct scenarios: the standard model with the presence of a 500 GeV massive Higgs boson and the standard model without presence of a Higgs boson. These samples were generated by the Monte-Carlo generator PHASE, whose main importance for vector boson scattering at high energies is its characteristic of calculating the complete matrix elements in leading order O(&#945;6). To analyze the viability of measuring the WW scattering at CMS, the simulated signal and background events were submitted to the CMS fast detector simulation, FAMOS. Background processes, WW+N jets, WZ+N jets, ZZ+N jets, W+N jets and tt+N jets, were studied and suppressed through kinematics region selection. Data analysis shows that the measurement of WW scattering in early stages of LHC will be very difficult, being necessary a larger luminosity, besides improvements on the analysis.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Este trabalho apresenta um estudo sobre o espalhamento W+W+ e W&#8722;W&#8722; para os primeiros anos de tomada de dados do experimento CMS do LHC, no CERN. O processo de espalhamento de bósons vetoriais, dentre os quais se inclui o espalhamento WW, é um processo chave para elucidação do mecanismo de quebra de simetria eletrofraca. Previsões teóricas mostram que as características cinemáticas do espalhamento de bósons vetoriais na escala T e V de energia devem depender significativamente do mecanismo que quebra a simetria eletrofraca. Este processo será analisado com dois objetivos principais: estudar a viabilidade de medi-lo em altas energias no CMS, e mostrar a sua sensibilidade ao mecanismo da quebra de simetria eletrofraca. Esta sensibilidade será mostrada através da análise de duas amostras de eventos correspondentes a dois cenários distintos: o modelo padrão com a presença de um bóson de Higgs de massa 500 GeV e o modelo padrão sem a presença do bóson de Higgs. Estas amostras foram geradas com o gerador de eventos PHASE, cuja principal importância para o estudo do espalhamento de bósons vetoriais em altas energias e a sua capacidade de calcular o elemento de matriz completo em ordem dominante O(&#945;6). Para se analisar a viabilidade de se medir o espalhamento WW no CMS, foi feita uma simulação do detector utilizando as amostras dos processos de sinal e dos principais processos de fundo através do pacote de simulação rápida do CMS, o FAMOS. Os processos de fundo, WW+N jatos, WZ+N jatos, ZZ+N jatos, W+N jatos e tt+N jatos, foram estudados e suprimidos através de seleções de regiões cinemáticas. A análise dos dados mostra que a observação do espalhamento WW na fase inicial do LHC será muito difícil, sendo necessária uma luminosidade maior, além de aprimoramento da análise. / This work presents a study of W+W+ and W&#8722;W&#8722; scattering for the first years of the CMS experiment data-taking at LHC, CERN. Vector boson scattering, including WW, is a key processes for probing electroweak symmetry breaking. Theoretical predictions show that kinematics characteristics of vector boson scattering at T e V scale must strongly depend on the electroweak symmetry breaking mechanism. This process is analyzed with two main objectives: viability study of performing this measurement at CMS and show its dependence on the electroweak symmetry breaking mechanism. This dependence is shown through an analysis with two event samples corresponding to two distinct scenarios: the standard model with the presence of a 500 GeV massive Higgs boson and the standard model without presence of a Higgs boson. These samples were generated by the Monte-Carlo generator PHASE, whose main importance for vector boson scattering at high energies is its characteristic of calculating the complete matrix elements in leading order O(&#945;6). To analyze the viability of measuring the WW scattering at CMS, the simulated signal and background events were submitted to the CMS fast detector simulation, FAMOS. Background processes, WW+N jets, WZ+N jets, ZZ+N jets, W+N jets and tt+N jets, were studied and suppressed through kinematics region selection. Data analysis shows that the measurement of WW scattering in early stages of LHC will be very difficult, being necessary a larger luminosity, besides improvements on the analysis.

The Standard Model (SM) is the fundamental theory describing elementary particles and their main interactions at typical energy scales at collider experiments, the electromagnetic, the weak, and the strong interactions. The more complex underlying structure describing the weak and the strong interactions in the SM compared to the electromagnetic interaction necessitates direct three-point and four-point interactions among the mediators of the weak and strong interactions, called gauge bosons. Such self-interactions do not exist for the gauge boson of the electromagnetic interaction, the photon. While the three-point interaction was studied in detail in earlier collider experiments, the four-point interaction is a fundamental prediction of the SM, which was not observed for the weak interaction when starting this study. One process, where both the three-point as well as the four-point interactions contribute is the scattering of electroweak gauge bosons W, Z, γ also referred to as vector boson scattering (VBS). In the SM, this scattering is mediated by gauge boson self-interactions, or via the exchange of a Higgs boson. The scattering contributions mediated by a Higgs boson are sensitive to the properties of the Higgs boson and the details of the mechanism in which the W and Z bosons acquire their masses, called electroweak symmetry breaking. At hadron colliders such as the Large Hadron Collider (LHC), VBS is observable in a final state with the decay products of two gauge bosons in combination with two jets. These jets have a distinct signature allowing for good suppression of backgrounds and consequently for studies of the complex final state despite the low cross-sections. The first evidence for a VBS process was presented based on the Run 1 dataset alone by the ATLAS collaboration in the WW → WW channel in the fully leptonic final state. The CMS collaboration published the first observation of VBS in the same channel using data from 2015 and 2016 of Run 2, which was later confirmed by the ATLAS collaboration with contributions by the author, e.g. in the modelling of WZ background processes and associated uncertainties. The second boson channel for which VBS was observed was the WZ/γ → WZ boson channel in the fully leptonic final state. This observation was published by the ATLAS collaboration with significant contributions by the author. The studied dataset was collected with the ATLAS detector at a centre-of-mass energy √s = 13 TeV during 2015 and 2016 of Run 2 of the LHC and amounts to an integrated luminosity of 36.1/fb. In this study, the dataset was re-analysed following the same overall approach but with improvements in several key aspects. A comprehensive overview of available setups for reliable simulations of the signal process is presented. In a modelling study of the available setups, modelling issues in the parton shower simulation of SHERPA and earlier versions of PYTHIA observed in earlier studies are confirmed. The best matrix-element accuracies in available setups are leading-order for the full VBS signal process and next-to-leading-order in the VBF approximation. For upcoming analyses, a leading-order calculation of the full process including an additional QCD emission merged with parton shower simulations is found to be most promising, before full next-to-leading order calculations become available for all boson channels in VBS. Additional emphasis is set on the modelling of backgrounds, mainly WZ diboson production in association with additional QCD emissions as well as the experimental background due to misidentified leptons. A data-driven approach is applied and studied in detail for a reliable estimate of the latter background. Significant improvements to the estimate, e.g. in the form of additional corrections, are found via dedicated tests of the self-consistency of the approach using simulations. Machine-learning algorithms in the form of Boosted-Decision-Trees (BDT) are trained and optimized for improved separation of the background and signal processes. Evidence for the signal process is found with a significance of 3.44 σ using the profile likelihood method in a binned maximum-likelihood fit. The fiducial cross-section is measured to be σ= 1.41 + 0.46 - 0.40(stat) + 0.38 - 0.28 (theo) ± 0.13 (sys) fb , which is in good agreement with the leading-order SM prediction of σ = 1.33 + 0.14 -0.15 fb.:1 Introduction 2 Theoretical Framework 3 Simulations and Modelling Studies 4 Experiment 5 Object and Event Selection 6 Background Estimation 7 Multi-variate Event Classification 8 Uncertainties 9 Cross-section Measurement 10 Conclusions & Outlook