The OPERA experiment is designed to perform first direct observation of $nu_{tau}$ appearance in an almost pure $nu_{mu}$ beam. The OPERA detector is a hybrid set-up which combines a lead/emulsion target with various electronic detectors. It is located in Gran Sasso Laboratory (LNGS), 730 km away from CERN where neutrino beam is produced. A good electron identification in the ECC brick would also allow OPERA to search for $nu_{mu}rightarrownu_{e}$ oscillations. We have studied electron identification in the Emulsion Cloud Chamber (ECC) brick which was exposed to CERN SPS H4 electron beam. Emulsion scanning was performed in LNGS scanning laboratory. FEDRA framework was used for the data analysis. In total, we have found 30 electron showers in the brick. The characteristics of each shower have been studied. The background base-track contamination in the shower was estimated as $20pm 4$. This is mainly due to shower overlap of electrons and passing through cosmic rays.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-04-25T19:24:06Z No. of bitstreams: 1 igorabrittacosta.pdf: 36138806 bytes, checksum: 83ce158c21ddf862f92969367375d57e (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-04-26T12:25:25Z (GMT) No. of bitstreams: 1 igorabrittacosta.pdf: 36138806 bytes, checksum: 83ce158c21ddf862f92969367375d57e (MD5) / Made available in DSpace on 2017-04-26T12:25:25Z (GMT). No. of bitstreams: 1 igorabrittacosta.pdf: 36138806 bytes, checksum: 83ce158c21ddf862f92969367375d57e (MD5) Previous issue date: 2016-02-22 / A identificação de elétrons é de fundamental importância para os grupos de física do experimento ATLAS, devido à presença destes no processo final de decaimento de partículas de interesse. Nesse ambiente de física de partículas, a probabilidade de ocorrência de elétrons relevantes aos estudos propostos são baixíssimas em relação às partículas que formam o ruído de fundo, exigindo dos grupos de performance do ATLAS algoritmos com índices de eficiência de detecção dos sinais de interesse e rejeição de ruído de fundo cada vez melhores. Nessa dissertação, os métodos aplicados na identificação de elétrons no experimento ATLAS serão revisados e possíveis otimizações serão avaliadas a partir dos dados produzidos pelo ATLAS. Concentrado no contexto offline, o trabalho reproduz o método baseado em verossimilhança e propõe uma melhoria com o uso da técnica multivariada conhecida como MKDE (do inglês, Multivariate Kernel Density Estimation), capaz de mitigar o erro inserido na consideração de dependência entre as variáveis discriminantes inserida pelo método de Likelihood atualmente em uso pelo ATLAS. Inicialmente, este trabalho se propõe a implementar o método de verossimilhança em uso, que se baseia em densidade univariadas usadas na reconstrução da densidade conjunta das variáveis discriminantes, e a estudar o impacto de possíveis parâmetros relacionados à implementação do algoritmo de estimação de densidades univariadas. Este método será então comparado com o método padrão do ATLAS conhecido como e/γ. Em uma segunda etapa, a implementação do MKDE é inserida através de uma comparação direta com o método univariado. / The electron identification is of fundamental importance for the ATLAS physics groups due to the presence of these in the final process of interest particles decay. In particle physics environment, the occurrence probability of relevant electrons to the proposed studies are very low compared to particles considered background, requiring ATLAS performance groups algorithms with identification efficiency index and background rejection each time better. In this dissertation, the methods applied in the electron identification in ATLAS experiment will be reviewed and possible optimizations will be evaluated from the data produced by the ATLAS experiment. Concentrated in the offline context, the work reproduces the method based on Likelihood and proposes an improvement with the use of multivariate technique known as MKDE (Multivariate Kernel Density Estimation), capable of mitigate the error inserted in consideration of dependence between discriminating variables entered by the method Likelihood currently in use by ATLAS. Initially, this work proposes to implement the method Likelihood in use, which is based on univariate density used in the reconstruction of the joint density of the discriminant variables, and to study the possible impact of parameters related to the implementation of univariate densities estimation algorithm. This method is then compared with the ATLAS standard method known as e/γ. In a second step the implementation of the MKDE is inserted through a direct comparison to the univariate method.

Le travail scientifique présenté dans cette thèse s’appuie sur des collisions proton proton, à 13 TeV dans le centre de masse, produite par le grand collisionneur de Hadron (LHC) et enregistrées entre 2015 et 2017 par le détecteur ATLAS. Après une brève introduction sur le programme de physique du LHC, le premier chapitre donne un aperçu complet du contexte et des motivations théorique. Ensuite une description complète du détecteur ATLAS et plus généralement de l’ensemble expérimental est donnée. Le troisième chapitre traite d’une des mesures des performances du calorimètre électromagnétique ATLAS, à savoir l’étude des efficacités identification électronique à l’aide de W se désintégrant en électrons et neutrinos.Dans les chapitres suivants, le coeur de cette thèse, la recherche et l’étude de la production associée de boson de Higgs avec une paire de quark top, appelée production ttH, est traitée dans le schéma du modèle Standard et au-delà. L’observation de la production ttH avec le détecteur ATLAS a été récemment annoncée en 2018 et représente une étape importante pour le domaine de la physique des hautes énergies. Afin d’élargir le spectre de cette analyse tth au-delà du SM, cet état final du canal 4L a aussi été étudié dans le cadre de la recherche de bosons de Higgs doublement chargés se désintégrant en W$^{\pm}$W$^{\pm}$, H$^{\pm \pm} \rightarrow $ W$^{\pm}$W$^{\pm}$. En conclusions, les perspectives sur les futurs résultats scientifiques dans le modèle Standard (SM) ainsi que au-delà de SM (BSM) qui pourraient être atteint en utilisant les statistiques complètes des Run1 et Run2 combinés sont donnés. / The scientific work presented in this thesis is based on proton proton collision produced, at 13 TeV in the center of mass, created by the Large Hadron Collider (LHC) and recorded between 2015 and 2017 by the ATLAS detector.After a short introduction on the physics program at LHC, the first chapter gives a comprehensive overview of the theoretical context and motivation. Then a complete description of the ATLAS detector and more generally the experimental setup is given with a highlight on the different physics objects used in this research.The third chapter is dealing with a measure of the performances of the ATLAS electromagnetic calorimeter, namely the study of the electron identification efficiencies using W decaying into electrons and neutrinos events.In the following chapters, the core of this thesis work, the search and study of the associated Higgs boson production with top quark pair, so-called ttH production, within the Standard Model schema and beyond is treated. The observation for ttH production with the ATLAS detector recently announced in 2018 represents a significant milestone for the High-Energy Physics field. In order to broaden the spectrum of this ttH analysis beyond the SM, this 4L channel final states was also studied in the context of the search for doubly charged Higgs boson decaying into W±W±, H±±→W±W±.In conclusions, future prospects in Standard Model (SM) as well as Beyond SM (BSM) scientific results that could be reached using the full Run1 and Run2 combined available statistics are given.