Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal

This work presents a study of the discovery potential for the neutral supersymmetric Higgs bosons h/A/H decaying to tau pairs with the ATLAS experiment at the LHC. The study is based on Monte Carlo samples which are scaled to state-of-the-art cross sections. The analyses are designed assuming an integrated luminosity of 30 1/fb and a center-of-mass energy of sqrt(s) = 14 TeV. The results are interpreted in the mmax h benchmark scenario. Two final states are analyzed: The dileptonic channel where the two tau leptons decay to electrons or muons and the lepton-hadron channel where one tau decays to an electron or muon and the other tau decays to hadrons. The study of the dilepton channel is based completely on the detailed ATLAS simulation, the analysis of the lepton-hadron channel is based on the fast simulation. The collinear approximation is used to reconstruct the Higgs boson mass and its performance is studied. Cuts are optimized in order to discriminate the signal from background and to maximize the discovery potential given a certain Higgs boson mass hypothesis. In the lepton-hadron channel the selection is split into two analyses depending on the number of identified b-jets. Procedures to estimate the dominant backgrounds from data are studied. The shape and normalization of the Z to tautau background are estimated from Z to leptonlepton control regions. The ttbar contributions to the signal regions are estimated from ttbar control regions. The individual analyses are combined and sensitivity predictions are made depending on the Higgs boson mass mA and the coupling parameter tanβ. The light neutral MSSM Higgs bosons with mA = 150 GeV can be discovered when at least tanbeta = 11 is realized in nature. The heavy neutral MSSM Higgs bosons with mA = 800 GeV can be discovered for tanbeta ≥ 44. However, due to the large width of the reconstructed Higgs boson mass and the mass degeneration, only the sum of at least two of the three Higgs boson signals will be visible.

Cette thèse présente une mesure de la section efficace de production du quark-top célibataire en voie t avec 1,04~fb^{-1} de données recueillies par le détecteur ATLAS au LHC à partir de collisions proton-proton d'énergie centre de masse sqrt(s) = 7TeV. Les événements sélectionnés contiennent un lepton, de l'énergie transverse manquante, et deux ou trois jets, l'un d'eux étant étiqueté comme étant issu d'un quark-b. Le modèle pour le bruit de fond se compose des processus multijets, W+jets et production de paires de quarks top ainsi que de contributions moindres venant d'événements Z+jets et diboson. En utilisant une méthode de coupures et de comptage basée sur la distribution d'un discriminant multivarié construit avec des arbres de décision stimulés, la section efficace de production de quark-top célibataire en voie t a été mesurée. La valeur sigma_ {t} = 97,3^{30,7}_{-30,2}~pb a été obtenue. Ce résultat est en bon accord avec la prédiction du Modèle Standard. En supposant que les éléments de la matrice CKM reliee au quark-top obéissent à la relation |Vtb|>>|Vts|, |V_td|, la force du couplage W-t-b est extraite de la section mesurée, |Vtb| = 1,23^{+0,20}_{-0,19}. Si on suppose que |Vtb|<1, une limite inférieure |Vtb|>0.61 est obtenue avec un niveau de confiance de 95%. / This thesis presents a measurement of the cross section of t-channel single top-quark production using 1.04~fb^{-1} data collected by the ATLAS detector at the LHC with proton-proton collision at center-of-mass sqrt(s)=7TeV. Selected events contain one lepton, missing transverse energy, and two or three jets, one of them b-tagged. The background model consists of multijets, W+jets and top-quark pair events, with smaller contributions from Z+jets and diboson events. By using a cut and count method based on the distribution of a multivariate discriminant constructed with the boosted decision trees, the cross section of t-channel single top-quark production is measured: sigma_{t}= 97.3^{+30.7}_{-30.2}~pb, which is in good agreement with the prediction of the Standard Model. Assuming that the top-quark-related CKM matrix elements obey the relation |Vtb|>>|Vts|, |V_td|, the coupling strength at the W-t-b vertex is extracted from the measured cross section, |Vtb| = 1,23^{+0,20}_{-0,19}. If it is assumed that |Vtb|<1, a lower limit of |Vtb|>0.61 is obtained at the 95% confidence level.

Le XXe siècle a marqué le succès de la construction du modèle standard de la physique des particules. Elaborée entre les années 1930 et 1970, cette théorie des particules élémentaires et des interactions électromagnétique, faible et forte a depuis été abondamment vérifiée auprès des collisionneurs tels que le LEP et le Tevatron. Malgré ce succès, certaines questions laissées en supsens ont nécessité l'élaboration de nouvelles théories permettant de dépasser le cadre du modèle standard. Parmi ces théories nombreuses sont celles prédisant l'existance d'un nouveau boson Z' à l'échelle du TeV. Les données du LHC, recueillies depuis son démarrage à l'automne 2008, offrent une nouvelle fois l'opportunité de confronter le modèle standard à ses prédictions et de rechercher les signatures de l'existence de nouvelle physique jusqu'à des énergies inégalées. Le travail mené au sein de l'expérience ATLAS au cours de ces quatres premières années s'est ainsi orienté autour de la compréhension du détecteur et de l'analyse des premières données. Cette thèse couvre ces deux aspects. La première partie du travail présenté revient ainsi sur la mise en évidence d'une pathologie de l'électronique de lecture du calorimètre à argon liquide d'ATLAS ainsi que sur l'étude de larges déviations cohérentes du bruit observées depuis sa mise en service. La mise en place d'une stratégie de préservation des données collectées y est détaillée. La seconde partie de ce manuscrit se concentre sur la recherche d'un nouveau boson Z'. Si tant est qu'une telle particule existe, sa décroissance en un électron et un positron devrait donner lieu à l'apparition d'une nouvelle résonance massive dans le spectre en masse invariante diélectron. Les performances de reconstruction et d'identification des électrons, particulièrement à haute impulsion transverse, sont étudiées. L'analyse des 4.9 fb-1 de données collectées en 2011 est décrite. En l'absence de déviation significative par rapport aux prédictions du modèle standard, le spectre en masse invariante diélectron est réinterprété afin de dériver les limites sur l'existence de nouveaux bosons issus de théories de grande unification (E6) et sur l'existence d'un boson de type SSM. Ces limites et celles obtenues par l'expérience CMS sont à l'heure actuelle les plus contraignantes quant à l'existence de ces nouveaux bosons. / The Standard Model of particle physics has known a tremendous rise during the twentieth century. Built up, from the early 1930s to the 1970s, this theory describing elementary particles and their interactions (electromagnetic, weak, strong) has now been intensivly tested by LEP and Tevatron colliders. Besides its succes, some problems remain and have lead to new theories attempting to go beyond the standard model. Many of them are predicting the existence of a new gauge boson Z', which is supposed to be observed at the TeV scale. Data recorded by the LHC since automn 2008 are a new opportunity to check the consistency of the Standard Model and to search for new physics evidence. Work that has been done by the ATLAS collaboration during the last four years has focused on understanding detector's behaviour and analysing the very first collected collisions. This thesis is reflecting these two aspects. Therefore, the first part of this thesis describes the caracterisation of a pathology of ATLAS liquid argon calorimeter electronics and of coherent noise bursts that have both been observed since the beginning of ATLAS operation. The policy deployed to preserve data quality is also detailled. The second part is focusing on the search for new Z' gauge boson. In case this particle was to exist, its decay into an electron and a positron would lead to a new massive resonance in the dielectron invariant mass spectrum. Therefore electron reconstruction and identification performances are closely looked at, especially at high transverse momentum. Analysis made on the 4.9 fb-1 of collected data is reported. As no significant excess with respect to Standard Model predictions is observed, the dielectron invariant mass spectrum is interpreted to derive mass limits concerning the existence of new Z' gauge bosons appearing in grand unification theories (E6) and effective sequential standard model (SSM). These limits and those derived by the CMS collaboration are the best ever set on such new bosons.

Made available in DSpace on 2016-08-29T15:08:51Z (GMT). No. of bitstreams: 1 tese_5843_Dissertação Renato Aurelio.pdf: 3196574 bytes, checksum: 3ef26b4483cdd9f0a941752d7d7ea03a (MD5) Previous issue date: 2012-08-28 / Este estudo, de natureza dialetológica, é realizado no âmbito da Geografia Linguística. Desse modo, é feita uma abordagem sobre a constituição da Dialetologia, com ênfase nos estudos implementados no Brasil, evidenciando-se o período pré-geolinguístico e as quatro fases dos estudos dialetais no país, todos fundamentais para a proposição do Projeto ALiB. O estudo apresenta um panorama sobre os atlas linguísticos brasileiros publicados e em andamento no Brasil, dentre os quais, o Atlas Prévio dos Falares Baianos (APFB) e o Atlas Linguístico do Espírito Santo (ALES), cujas cartas são cotejadas, para verificação das possíveis influências da Bahia sobre o Espírito Santo. Considerando-se que o estudo se baseia na análise das cartas lexicais dos atlas supracitados, bem como, de outros que registram as lexias selecionadas, discute-se um pouco sobre a relação entre léxico e cultura. Há uma breve descrição sobre a constituição do estado do Espírito Santo, seu processo de colonização e povoamento. A hipótese do estudo baseia-se nos postulados de Zágari (2005), que constata a ocorrência do falar baiano ao norte de Minas Gerais e de Rodrigues (2008), que discute sobre a possibilidade de rever a classificação feita por Nascentes (1953) para os dialetos brasileiros, ao verificar a ocorrência de lexias citadas por Rossi (1963) em solo capixaba. Na análise e discussão, são apresentados os resultados do cotejamento oito pares de cartas lexicais adaptadas do APFB (ROSSI, 1963) e do ALES (RODRIGUES, 2008), sendo que cinco pares revelam a ocorrências comuns a outros atlas e três pares caracterizam uma possível influência baiana nos falares capixabas. / This study consists on a research in the area of dialects conducted within the Linguistic Geography. Thus it is made an approach about the constitution of Dialectology, with emphasis on studies implemented in Brazil, in the period pregeolinguistic and the four phases of dialect studies in the country, all of them fundamental to the proposition of the Project Alib. The study provides an overview of the Brazilian linguistic atlas published and in progress in Brazil, including the Atlas of Early “Baianos” Speeches (APFB) and the Linguistic Atlas of the Espírito Santo State (ALES), whose letters are compared to check the possible influence of Bahia on the other state. Considering that the study is based on an analysis of the letters of lexical atlas mentioned, as well as others which record the lexias selected, it is also discussed a little about the relationship between lexicon and culture. There is a brief description of theconstitution of Espírito Santo State, the process of colonization and settlement. The hypothesis of the study is based on Zagari’s postulates (2005), which notes the occurrence of speeches from Bahia in north of Minas Gerais and Rodrigues (2008), who discusses the possibility of revising the classification made by Nascentes (1953) to the Brazilian dialects, verifying the occurrence of lexias mentioned by Rossi (1963) in Espírito Santo territory. In the analysis and discussion are presented the results of the comparison of eight pairs of lexical letters adapted from APFB (ROSSI, 1963) and ALES (RODRIGUES, 2008), considering that five pairs reveal the common occurrences in other atlas and three pairs characterize a possible “Bahiana” influence in the speech of Espirito Santo natives.

Made available in DSpace on 2014-06-11T19:32:18Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-10-17Bitstream added on 2014-06-13T20:43:12Z : No. of bitstreams: 1 moreira_mr_dr_rcla.pdf: 2967010 bytes, checksum: a3a8fd8d971c6b62113182b986e3ed84 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Os movimentos de massa na Serra do Mar são alvos de muito interesse e estudo devido à alta incidência e aos conseqüentes impactos ambientais e econômicos. Portanto, reunir várias informações sobre movimentos de massa, e disponibilizá-los como um produto de fácil aquisição e de navegabilidade para o conhecimento de alunos de graduação, é o desafio desse trabalho. Como área de aplicação, escolheu-se o município de Cubatão, pela significativa incidência de escorregamentos e pela importância da região no contexto nacional, frente a aspectos econômicos e ambientais. Desta forma, o objetivo principal é produzir um Atlas Multimídia sobre os processos de movimentos de massa, como contribuição ao ensino de graduação, nas áreas de Ciências da Terra e Engenharia e avaliar a aplicabilidade da linguagem SVG (Scalable Vectorial Graphics) na produção de mapas interativos. Foi efetuada uma consulta a docentes e alunos da área de Ciências da Terra, sobre o interesse na utilização de material didático multimídia como apoio ao ensino e aprendizado e os resultados obtidos mostraram o claro interesse deste público no desenvolvimento do material .O Atlas interativo elaborado, voltado especificamente a escorregamentos, usando interfaces gráficas na linguagem SVG,mostrou que é possível a publicação de aplicações cartográficas interativas utilizando o SVG. Acredita-se que a utilização deste tipo de material como apoio ao ensino e aprendizado seja uma tendência crescente, impulsionada pelos avanços tecnológicos e pela forte inserção da informática em todos os setores de atividade. Inseridos neste contexto, os atuais alunos, desde muito cedo, vivem a informática nos seus cotidianos e a inserção destes recursos em sala de aula torna os cursos mais atrativos para este público. / Mass movements of Serra do Mar are the subject of much interest and study due to high incidence, the consequent environmental and economic impacts. For these reasons, to get some information about mass movements and make them available as a product of easy acquisition and navigability for the knowledge of undergraduate students, it is the challenge of this work. The study area was the Cubatão city by the significant incidence of slip and the importance of the region in the national context, in face of economic and environmental aspects. Thus, the main goal is to produce an Atlas Multimedia about processes of mass movements, to contribute to the education of undergraduate students in Earth Sciences and Engineering areas and evaluate the applicability of the SVG (Scalable Vectorial Graphics) language in the production of interactive maps. It was done a questionnaire for the purpose of gathering information from teachers and students in Earth Sciences area, about the interest in the use of multimedia educational materials to support teaching and learning. The results showed clear interest of the public in developing the material. The Interactive Atlas prepared, specifically to landslide, using graphical interfaces in the SVG language, showed that it is possible to publish interactive mapping applications using SVG. It was believed that the use of such material to support teaching and learning is a growing trend, driven by technological advances and the strong integration of computer science technology in all sectors of this activity. In this context, the current students, from an early age, living in their everyday computing and the integration of these resources in the classroom make the courses more appealing to the public.

Introduction : La stimulation électrique directe basse fréquence est pratiquée sur des patients épileptiques pharmaco-résistants implantés avec des électrodes profondes. Elle induit de potentiels évoqués cortico-corticaux (PECC) qui permettent d’estimer la connectivité in vivo et ont permis de caractériser des réseaux locaux. Pour estimer la connectivité à l’échelle du cortex, le projet multicentrique F-TRACT vise à rassembler plusieurs centaines de patients dans une base de données pour proposer un atlas probabiliste de tractographie fonctionnelle.Méthodes : La construction de la base de données à nécessité la mise en place technique de pipelines de traitement semi-automatiques pour faciliter la gestion du nombre important de données de stéréo-électroencéphalographie (SEEG) et d’imagerie. Ces pipelines incluent des nouvelles méthodes de traitement du signal et d’apprentissage automatique, qui ont été développées pour identifier automatiquement les mauvais contacts et corriger l’artefact induit par la stimulation. Les analyses de groupe se sont basées sur des métriques des PECC et des cartes temps-fréquences des réponses à la stimulation.Résultats : La performance des méthodes développées pour le projet a été validée sur des données hétérogènes, en termes de paramètres d’acquisition et de stimulation, provenant de différents centres hospitaliers. L’atlas a été généré à partir d’un échantillon de 173 patients, fournissant une mesure de probabilité de connectivité pour 79% des connexions et d’estimer des propriétés biophysiques des fibres pour 46% d’entre elles. Son application à une sous-population de patients a permis d’étudier les réseaux impliqués dans la génération de symptômes auditifs. L’analyse de groupe oscillatoire a mis en avant l’influence de l’anatomie sur la réponse à la stimulation.Discussion : Cette thèse présente une méthodologie d’étude des PECC à l’échelle du cortex cérébral, utilisant des données hétérogènes en termes d’acquisition, de paramètres de stimulation et spatialement. L’incrémentation du nombre de patients dans l’atlas généré permettra d’étudier les interactions cortico-corticales de manière causale. / Introduction: Low-frequency direct electrical stimulation is performed in drug-resistant epileptic patients, implanted with depth electrodes. It induces cortico-cortical evoked potentials (CCEP) that allow in vivo connectivity mapping of local networks. The multicentric project F-TRACT aims at gathering data of several hundred patients in a database to build a propabilistic functional tractography atlas that estimates connectivity at the cortex level.Methods: Semi-automatic processing pipelines have been developed to handle the amount of stereo-electroencephalography (SEEG) and imaging data and store them in a database. New signal processing and machine-learning methods have been developed and included in the pipelines, in order to automatically identify bad channels and correct the stimulation artifact. Group analyses have been performed using CCEP features and time-frequency maps of the stimulation responses.Results: The new methods performance has been assessed on heterogeneous data, coming from different hospital center recording and stimulating using variable parameters. The atlas was generated from a sample of 173 patients, providing a connectivity probability value for 79% of the possible connections and estimating biophysical properties of fibers for 46% of them. The methodology was applied on patients who experienced auditory symptoms that allowed the identification of different networks involved in hallucination or illusion generation. Oscillatory group analysis showed that anatomy was driving the stimulation response pattern.Discussion: A methodology for CCEP study at the cerebral cortex scale is presented in this thesis. Heterogeneous data in terms of acquisition and stimulation parameters and spatially were used and handled. An increasing number of patients’ data will allow the maximization of the statistical power of the atlas in order to study causal cortico-cortical interactions.

Le modèle standard (SM) est une théorie auto cohérente expliquant les particules élémentaires et leurs interactions. Le grand collisionneur de hadron ou Large Hadron Collider (LHC) a été construit au CERN pour mesurer avec précision les paramètres du SM et en chercher la dernière particule, le boson de Higgs. Le détecteur polyvalent ATLAS, mis en place auprès d’un de ses points d’interaction, couvre la quasi-totalité de l’angle solide et peut détecter les particules issues de collisions proton-proton (pp). Un très grand nombre d’événements ttbar y sont produits et permettent des mesures précises des propriétés du quark top. Les événements contenant exactement deux leptons isolés de charges opposées, au moins deux jets de haute impulsion transverse et une grande énergie manquante, sont considérés comme événements signal ttbar di-leptonique. Pour supprimer le fond, au moins un jet doit être étiqueté de type b. Ce canal a un rapport de branchement plus faible que d’autres canaux mais ses caractéristiques permettent de rejeter significativement le fond QCD et WJet.Cette thèse présente la mesure différentielle de la corrélation de spin ttbar et de l’hélicité du boson W avec les 4.6 fb-1 de données de collisions pp à 7TeV enregistrées en 2011. Les deux mesures appliquent une méthode bayésienne de dé-convolution pour extraire la «vraie» distribution de parton de celle «observée». La régularisation est étudiée dans les différentes analyses. Le spectre différentiel de corrélation de spin combiné de saveur dé-convolué est en accord avec les prédictions NLO SM. Les fractions F0, FL et FR, d’helicité combinée de saveur, du boson W sont également compatibles avec les valeurs NLO SM. / The Standard Model (SM) is a self-consistent theory that explains the elementary particles and interactions. To further confirm the SM theory, the Large Hadron Collider (LHC) was built at CERN to accurately validate the SM and search for the last SM particle, the Higgs boson. The multipurpose ATLAS detector is set up at one of the LHC interaction point. Nearly covering the whole solid angle, it detects particles over a wide range of energies with well-designed sub-detectors to record proton-proton (pp) collision up to a 14TeV center-of-mass energy and a luminosity of 1034 cm-2 s-1. A large number of ttbar events are produced and can be used for precise top quark property studies. Events that decay in exactly two opposite sign isolated leptons, at least two high transverse momentum jets and large missing energy are considered as di-leptonic t tbar signal events. To suppress the background, at least one of jets must be b-tagged. This channel has a lesser branching ratio with respect to other channels but its features allow to reject the QCD and W+jet backgrounds significantly.This thesis presents the differential measurement of ttbar spin correlation and W boson polarization using the 4.6 fb-1 7TeV pp collision data recorded in 2011. Both of the measurements apply Bayesian unfolding algorithm to extract the parton "true" spectrum from the "observed" one. The regularization is well studied in the different analyses. The combined unfolded spectrum of ttbar spin correlation agrees with the SM NLO prediction at differential level. The extracted W boson helicity combined results of F0, FL and FR fractions are also consistent with SM NLO values.

En Juillet 2012, les expériences ATLAS et CMS annoncent la découverte d'une nouvelle particule de masse 125 GeV, compatible avec le boson de Higgs prédit par le Modèle Standard. Pour établir la nature de ce boson de Higgs et la comparer au Modèle Standard, il est nécessaire de mesurer le complage du boson de Higgs au fermions. En particulier le quark top possède le plus fort couplage de Yukawa avec le boson de Higgs. Ce couplage est accessible par le processus de production d'un boson de Higgs en association avec une paire de quarks tops (ttH). Cette thèse présente la recherche d'évènement ttH où le boson de Higgs se désintègre en deux quark b dans les données du Run 2 recueillies en 2015 et 2016 par le détecteur ATLAS. La composition du bruit de fond ainsi que la mesure du signal ttH dans les données sont obtenues à partir d'un ajustemement statistique des prédictions aux données. Le bruit de fond tt+jets étant la plus grande source d'incertitudes sur le signal, une attention particulière est portée à sa description.La détection des jets issus de quarks b, appelé b-tagging, est primordiale pour l'analyse ttH(H->bb) dont l'état final contient quatre quarks b. Afin d'améliorer la compréhension des performances des algorithmes de b-tagging pour le Run 2, la définition des jets de saveur b dans les simulations Monte Carlo est revisitée. Les algorithmes standards du b-tagging ne permettant pas la différenciation des jets contenant un ou deux quarks b, une methode spécifique à été développée et est présentée dans cette thèse. / In July 2012, the ATLAS and CMS experiments announced the discovery of a new particle, with a mass about 125 GeV, compatible with the Standard Model Higgs boson. In order to assess if the observed particle is the one predicted by the Standard Model, the couplings if this Higgs boson to fermions have to be measured. In particular, the top quark has the strongest Yukawa coupling to the Higgs boson. The associated production of a Higgs boson with a pair of top quarks (ttH) gives a direct access to this coupling. The ttH process is accessible for the first time in the Run 2 of the LHC thanks to an upgrade of the detector and the increase of the center of mass energy to 13 TeV. This thesis presents the search for ttH events with the Higgs boson decaying to a pair of b-quarks using data collected by the ATLAS detector in 2015 and 2016. The description of the background and the extraction of the ttH signal in data are obtained by a statistical matching on predictions to data. In particular the tt+jets background is the main limitation to signal sensitivity and is scrutinized.The identification of jets originating from b-quarks, called b-tagging, is a vital input to the search of ttH(H->bb) events because of the four b-quarks in the final state. For Run 2 the definition of b-flavoured-jets in Monte Carlo simulations is revisited to improve the understanding of b-tagging algorithms and their performance. Standard b-tagging algorithms do not separate jets originating from a single b-quark from those originating from two b-quarks. Thus a specific method has been developed and is reviewed in this thesis.