Le boson de Higgs, qui est responsable de la brisure de symétrie électrofaible et de l’origine de la masse des particules, est le sujet central de la physique des particules d’aujourd’hui. J’ai travaillé sur le boson de Higgs se désintégrant en quatre leptons dans l’expérience ATLAS du LHC.Dans ma thèse, j’ai étudié le bruit de fond du canal H->ZZ^*->4l. Le signal de ce canal est très propre car il a quatre leptons dans l'état final. Il est donc important de maitriser son bruit de fond afin d'extraire le signal. J’ai travaillé à la réduction d’une des principales sources de bruit de fond: Z+ee->4leptons.En fin de thèse j’ai étudié un modèle au-delà du Modèle Standard: le modèle à deux doublets de Higgs (2HDM). Dans cette étude nous supposons que le boson de Higgs légers à la masse de la nouvelle particule détectée au LHC : 125 GeV. Aucun signal n’a été trouvé pour le boson de Higgs lourd et les limites sont données dans l’espace des paramètres de 2HDM. / Higgs boson which is responsible for the electroweak symmetry breaking and the origin of the particle mass is the core subject of particle physics today. I have worked on Higgs boson decaying into four leptons in the ATLAS experiment at LHC.In my thesis I have studied the background process to H->ZZ^*->4leptons signal. The signal of this channel is very clean because of the four leptons in the final state. Therefore, it is important to control the backgrounds to extract signal. I have worked to reduce one of the major background sources of Z+ee->4leptons process.At the end of my thesis, I discuss a model beyond the Standard Model: the two Higgs Doublets Model (2HDM). In this study I assume that the light Higgs is the new particle detected by the LHC with a mass of 125 GeV. No signal was found for the heavier Higgs and the limit is given in the parameter space of the 2HDM.

Reproduction de : Thèse de doctorat : Physique : Lyon 1 : 2004. / Titre provenant de l'écran titre. 129 réf. bibliogr.

Thesis (Ph. D.)--University of Chicago, Dept. of Mathematics, August 2003. / Includes bibliographical references. Also available on the Internet.

Orientador: Sérgio Ferraz Novaes / Banca: Manuel Drees / Banca: Vicente Pleitez / Banca: Carlos Ourívio Escobar / Banca: Takeshi Kodama / Resumo: 0 Modelo Padrão é, hoje em dia, a melhor formulação teórica para a descrição das interações eletrofracas. 0 acordo entre resultados experimentais e previsões teóricas é expressivo para acoplamentos entre bósons vetoriais e férmions. Porém, possuímos poucas informações sobre o bóson de Higgs, remanescente do mecanismo de quebra de simetria eletrofraca responsável pela geração das massas dos férmions e dos bósons vetoriais. Neste trabalho procuramos explorar alternativas para os acoplamentos do bóson de Higgs aos demais bósons da teoria através do uso de lagrangeanas efetivas. Examinamos as consequências destas novas interações em diversas reações envolvendo a produção e decaimento do bóson de Higgs em colisões elétron-pósitron e hadrônicas. 0 estudo dessas reações nos permite impor vínculos sobre as constantes de acoplamento destas novas interações, os quais são comparados com os limites experimentais das constantes de acoplamento da parametrização convencional dos auto-acoplamentos entre os bósons vetoriais IVWZ e W'gama'. / Abstract: The Standard Model is the best theoretical framework which describes the elec- troweak interactions. The agreement between experimental data and theoretical predictions is spectacular for the fermion-vector boson couplings. However, we have few information concerning the electroweak symmetry breaking sector of the theory. In this Work we explore diíferent possibilities for the couplings among the Higgs boson and the vector bosons of the theory through the use of the effective lagrangian formalism. We examine the consequences of these new interactions in several re- actions involving the Higgs boson production and decay at electron-positron and hadronic collisions. We analyze these reactions in order to impose bounds on the coupling constants of these new interactions. These bounds are compared with the experimental limits on the usual parametrization of the anomalous WWZ and WW'gama' / Doutor

This thesis concerns the study of extended Higgs sectors at future colliders. Such studies are well motivated since enlarged Higgs models are a necessity in many extensions of the Standard Model (SM), although these structures may be considered purely in the context of the SM, to be called the 'non-minimal SM'. The continuous theme of the thesis is the task of distinguishing between the (many) theoretically sound non-minimal Higgs sectors at forthcoming colliders. If a Higgs boson is found it is imperative to know from which model it originates. In particular, the possible differences between the Higgs sectors of the Minimal Supersymmetric Standard Model (MSSM) and the non-minimal SM are highlighted. Considered first are the detection prospects of light charged Higgs scalars (H(^±)) at e(^+)e(^-) colliders. The discovery of a H(^±) would provide unambiguous evidence for a non- minimal Higgs sector. We show that in certain (but not all)non-minimal models a light H(^±) may exist i.e. be within the mass range accessible at LEP2 (M(_H)(_ ±) ≤ Mw). In particular the MSSM requires M(_H±) ≥ Mw, and thus detection of a at LEP2 is strong evidence against the MSSM. We discuss ways of distinguishing between the models which may contain a light H(^±) by exploiting differences in the decay channels. Attention is then given to the neutral Higgs bosons of the non-minimal SM. It is possible that these particles may possess a greatly different phenomenology to that of the mammal SM and MSSM, and we explore the feasibility of observing these differences at LEP2 and the LHC It is found that distinct, sometimes spectacular signatures are possible. The thesis next considers a more exotic Higgs representation, namely that of Higgs triplets, and compares its phenomenology at LEP2 with that of the non-minimal models covered thus far The phenomenon of Higgs bosons decoupling from the fermions(fermiophobia) arises naturally in the above triplet model, and this concept is studied in more depth in the final chapter. It is emphasized that such particles are not possible in the MSSM.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. Johannesburg, 2014. / This thesis presents multiple studies contributing to the research conducted at the ATLAS experiment at the CERN facility in Switzerland. The areas of contribution include the ATLAS physics validation developments and the Standard Model Higgs boson decaying to two tau leptons search e ort. A section outlining the use and maintenance of the ATLAS TauValidation package details contributions made towards the ATLAS physics validation program.

Reproduction de : Thèse de doctorat : Physique nucléaire : Lyon 1 : 2002. / Titre provenant de l'écran titre. 62 réf. bibliogr.

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Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 147-150).

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Supervisor: Duane A. Dicus. Vita. Includes bibliographical references.