Ce mémoire accentue des aspects du programme de recherche pour un futur collisionneur linéaire des électrons et positrons permettant de faire de la physique de précision à l'echelle de TeV où l'apparition des phénomènes au-delà du Modèle Standard de la physique de particules est attendue. La proposition la plus mature pour une telle machine est l'International Linear Collider (ILC) conçue pour des énergies dans le centre de masse entre 90 GeV et 1 TeV. Les résultats obtenus avec des expériences de précision précédentes suggèrent l'existence du boson de Higgs ayant une masse d'environ 120 GeV. En assumant des paramètres nominaux pour les faisceaux et la luminosité, l'ILC est prometteur d'atteindre une précision de 2-3% sur la section efficace de la Higgs-strahlung et d'environ 30 MeV sur la masse du boson de Higgs. Les détecteurs qui seront opérés au sein de l'ILC comprendront des calorimètres à haute granularité. Ce nouveau type de calorimètre constitue l'outil principal pour atteindre une résolution en énergie des jets de 30%/\sqrt{E}. Le calorimètre électromagnétique sera composé par tungstène comme matériel absorbant et il est actuellement favorisé d'employer des diodes de silicium comme matériel actif. Le document décrit des détails du programme de R&D pour ce calorimètre par rapport à la mécanique et du développement de l'électronique frontale qui sera integrée dans les couches du calorimètre. En plus, l'état actuel du développement des galettes de silicium est abordé. Les résultats obtenus dans les campagnes de test en faisceau avec un premier prototype confirment les paramètres appliqués dans les études de la ''Letter of Intent'' publiée par le groupe de concept ILD en 2009.

In partial fulfillment of the requirements for the "Habilitation a Diriger des Recherches" at Pierre et Marie Curie University in Paris

The Higgs boson has an important role in the theoretical formulation of the standard model of fundamental interactions. Symmetry breaking of the vacuum via the Higgs field allows the gauge bosons of the weak interaction and all fermions to acquire mass in a way that preserves gauge-invariance, and thus renormalizablility. The Standard Model can accommodate an arbitrary number of Higgs fields with appropriate charge assignments. To explore the effects of multiple Higgs particles, the SU(2)-multi-Higgs model is studied using lattice simulations, a non-perturbative technique in which the fields are placed on a discrete space-time lattice. The formalism and methods of lattice field theory are discussed in detail. Standard results for the SU(2)-Higgs model are reproduced via Monte Carlo simulations, in particular the single-Higgs phase structure, which has a region of analytic connection between the symmetric and Higgs phases. The phase structure of the SU(2)-multi-Higgs model is explored for the case of N >= 2 identical Higgs fields. There is no remaining region of analytic connection between the phases, at least when interactions between different Higgs flavours are omitted. An explanation of this result in terms of enhancement from overlapping phase transitions is explored for N = 2 by introducing an asymmetry in the hopping parameters of the Higgs fields.

The Higgs boson has an important role in the theoretical formulation of the standard model of fundamental interactions. Symmetry breaking of the vacuum via the Higgs field allows the gauge bosons of the weak interaction and all fermions to acquire mass in a way that preserves gauge-invariance, and thus renormalizablility. The Standard Model can accommodate an arbitrary number of Higgs fields with appropriate charge assignments. To explore the effects of multiple Higgs particles, the SU(2)-multi-Higgs model is studied using lattice simulations, a non-perturbative technique in which the fields are placed on a discrete space-time lattice. The formalism and methods of lattice field theory are discussed in detail. Standard results for the SU(2)-Higgs model are reproduced via Monte Carlo simulations, in particular the single-Higgs phase structure, which has a region of analytic connection between the symmetric and Higgs phases. The phase structure of the SU(2)-multi-Higgs model is explored for the case of N >= 2 identical Higgs fields. There is no remaining region of analytic connection between the phases, at least when interactions between different Higgs flavours are omitted. An explanation of this result in terms of enhancement from overlapping phase transitions is explored for N = 2 by introducing an asymmetry in the hopping parameters of the Higgs fields.

This thesis presents a measurement of the mass, natural width, and signal strength, defined as the yield normalized to the Standard Model prediction, of the Higgs boson in the \(H \rightarrow ZZ^{(*)} \rightarrow 4l\) decay channel using an approach which utilizes event-by-event detector response information. The measurement is performed on p-p collision data recorded by the ATLAS experiment at the CERN Large Hadron Collider. The data corresponds to an integrated luminosity of \(25 fb^{-1}\) with center-of-mass energies of 7 TeV and 8 TeV. The measured mass of the Higgs boson is \(m_H = 124.57_{-0.43}^{+0.48} GeV\). The signal strength was estimated at \(\mu = 1.76_{-0.37}^{+0.46}\). Finally, the natural width of the Higgs was determined to be < 2.6 GeV with 95% confidence. The event-by-event approach used in this analysis involves the parameterization of the behavior of single leptons in the ATLAS detector and the convolution of a mass response with the Higgs truth distribution to derive the reconstruction level signal model. / Physics

No description available.

The discovery of a charged Higgs boson (H±) would be a clear indication for physics beyond the Standard Model. This thesis describes searches for charged Higgs bosons with the ATLAS experiment at CERN’s Large Hadron Collider (LHC). The first data collected during the LHC Run 1 is analysed, searching for a light charged Higgs boson (mH±&lt;mtop), which decays predominantly into a tau-lepton and a neutrino. Different final states with one or two leptons (electrons or muons), as well as leptonically or hadronically decaying taus, are studied, and exclusion limits are set. The background arising from misidentified non-prompt electrons and muons was estimated from data. This so-called "Matrix Method'' exploits the difference in the lepton identification between real, prompt, and misidentified or non-prompt electrons and muons. The Matrix Method is used in all charged Higgs boson searches in this thesis. In 2024 the LHC will be upgraded into a High Luminosity LHC (HL-LHC). The ATLAS detector is expected to collect around 300 fb-1 of collision data until 2022, whereas the HL-LHC will deliver about 250-300 fb-1 of data per year. This will increase the mean number of interactions per bunch crossing, resulting in larger particle fluxes. This puts challenging requirements on the electronics. In order to keep trigger and data rates at manageable levels, new trigger concepts require more intelligence at early stage which possibly results in more cables and connectors, inside the detector which lead to degraded performance of the detector system. This thesis presents new concepts using wireless technology at 60 GHz, in order add more data links inside the detector system without adding much material. Patch antennas have been developed, operating at 60 GHz. Manufacture methods have been investigated, and the fabrication tolerances and bandwidth of these antennas have been studied. Also, concepts of using passive repeaters have been investigated, to make the 60 GHz signal pass boundaries. These repeaters can be used to connect intelligence inside the detector, but also for reading out data from the whole detector radially.

This thesis outlines the search for neutral Higgs bosons in a mass range of m_H/A = 200 GeV − 1.2 TeV, decaying to a pair of hadronically decaying tau leptons. The search is performed using &radic;s = 13 TeV proton-proton collision data, corresponding to an integrated luminosity of 3.21 fb^-1, recorded by the ATLAS detector. No excess over the predicted Standard Model background is observed and upper limits are placed on the production cross section times branching fraction as a function of the mass of the scalar resonance. When combined with the results of the analysis where one of the tau leptons decays to either a muon or electron, the 95% confidence level upper limit on the cross section times branching fraction ranges from 1.4 pb at m_H/A = 200 GeV to 0.025 pb at m_H/A = 1.2 TeV for a scalar boson produced via gluon-gluon fusion, and 1.6 pb at m_H/A = 200 GeV to 0.028 pb at m_H/A = 1.2 TeV for a scalar boson produced via b-associated production. The results are interpreted in the Minimal Supersymmetric extension to the Standard Model (MSSM) as a limit on the value of tan&beta;, as a function of the mass of the neutral CP-odd MSSM Higgs boson. In the mmod+ scenario, the 95% confidence level upper limit is tan&beta; &LT; 7.6 for m_A = 200 GeV, and tan&beta; &LT; 47 for m_A = 1 TeV. For the mass range m_A &GT; 500 GeV, the upper limit on tan&beta; is improved in comparison to previous ATLAS searches.

De nombreux modèles, au delà du modèle standard, prédisent l’existence de résonances se désintégrant en deux photons. La signature expérimentale très spécifique, associée à l’excellente résolution en masse et à la distribution du bruit de fond bien comprise, en font un canal roi pour la recherche de nouvelle physique.Ce document présente la recherche de nouvelles particules se désintégrant en une paire de photons effectuée auprès du Grand Collisionneur de Hadrons (LHC) du CERN avec le détecteur ATLAS. L’ensemble des données de collisions de protons, accumulées en 2015 et 2016, à l’énergie dans le centre de masse de 13 TeV, correspond à 37 fb-1.J’ai développé la méthode et la procédure pour décrire un éventuel signal, en simulant des résonances de masses et largeurs variables. Avec ce modèle j’ai pu calculer l’efficacité de sélection et donner une interprétation statistique des résultats. Cette analyse a permis de montrer que les données collectées sont en accord avec les prédictions du modèle standard. Des limites sur la section efficace de production couplée au rapport d’embranchement en deux photons, en fonction de la masse et de la largeur de la résonance considérée sont présentées.Le calorimètre électromagnétique de ATLAS joue un rôle clé pour cette analysis di-photon. L’excellente résolution en énergie permet de reconstruire électrons et photons avec une précision de l’ordre de 1% aux énergies considérées. J’ai pris part au fonctionnement du calorimètre lors du démarrage du run-2 et décris ici mes contributions.Finalement, un des points clé pour la mesure de la masse du boson de Higgs est la qualité de la calibration de l’énergie des photons. J’ai développé une approche qui permet de prendre en compte l’impact du développement latéral des gerbes électromagnétiques sur la reconstruction de l’énergie. Cette méthode permettra de réduire l’erreur systématique sur la mesure de la masse du boson de Higgs, mesurée par son mode de désintégration en deux photons. / New high-mass states decaying into two photons are predicted in many extensions of the Standard Model (SM). The diphoton final state provides a clean experimental signature with excellent invariant mass resolution and well-known smooth backgrounds.This document presents a search for new particles with diphoton final state at the Large Hadron Collider with the ATLAS detector. The pp collision data used were collected during 2015 and 2016 runs with a center-of-mass energy of 13 TeV. The total corresponding luminosity is ~37 fb-1.In this thesis, I show my contribution to the search of scalar particle. The studies of signal modeling for different mass and width hypothesis will be described in details. The estimation of selection efficiencies and statistical interpretations of results are performed.The data are consistent with the Standard Model background-only hypothesis. Limits on the production cross section times branching ratio to two photons of such resonances as a function of the resonance mass and width are presented.The Liquid Argon electromagnetic calorimeter plays a crucial role in the diphoton analysis. The excellent energy resolution allows to reconstruct objects with high precision. The contribution to operation of LAr calorimeter and its online software will be discussed.The calibration of the electron and photon energy measurements with the electromagnetic calorimeter is performed. The systematic uncertainties related to energy response are one of the largest contribution limiting the precision measurements of the Standard Model Higgs boson mass. The approach to improve the energy response taking into account lateral shower shape development is applied in the calibration procedure.

The Large Hadron Collider (LHC) has provided, and will continue to provide, data for collisions at the highest energies ever seen in a particle accelerator. A strong knowledge of the properties of amplitudes for Quantum Chromodynamics in the High Energy Limit is therefore important to interpret this data. We study this limit in the context of the High Energy Jets (HEJ) formalism. This formalism resums terms in the perturbative expansion of the cross-section that behave like αn/s log (s/-t)ⁿ¯¹, which are enhanced in this limit. Understanding this region is particularly important in certain key analyses at the LHC: for example, Higgs-boson- plus-dijet analyses where cuts are applied to pick out events with a large mjj and in many searches for new physics. In this thesis, we discuss two directions in which HEJ's accuracy has been improved. Firstly, we look at adding descriptions of partonic subprocesses which are formally sub-leading in the jet cross-section but Leading Logarithmic (LL) in the particular subprocess itself. This required the derivation of new effective vertices that describe the emission of a quark/anti-quark pair in a way that is consistent with the resummation procedure. The inclusion of such processes reduces HEJ's dependence on fixed-order calculations and marks an important step towards full Next-to-Leading Logarithmic (NLL) accuracy in the inclusive dijet cross-section. The second extension was to improve our description of events involving the emission of a Higgs boson along with jets. Specifically, we derive new effective vertices which keep the full dependence on the quark mass that appears in the loops that naturally arise in such amplitudes. The formalism is also simple enough to allow for any number of extra nal state jets in the process. Therefore, HEJ is unique in its ability to provide predictions for high-multiplicity Higgs-plus-jets processes with full nite quark mass e ects. Such a calculation is far beyond the reach of any xed order approach.