Diboson Higgs and EWK measurements and triple gauge couplings with ATLAS and CMS

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Mesure des dibosons ZZ avec le détecteure ATLAS auprès du LHC et Etude des sondes du champ magnetique toroidal

Les particules élémentaires ainsi que leur interactions sont décrites par le Modèle Standard. Malgré son grand succès, il y a encore des questions à répondre. Dans cette thése, le processus du Modèle Standard ZZ, lorsque les deux bosons Z se désintègrent en paires de leptons, a été étudié. Les données utilisées ont été prises par le détecteur ATLAS durant l'année 2012, ce qui correspond à une luminosité intégrée de 20 fb-1. L'énergie dans le centre de masse était de 8 TeV. Tous les éléments de l'analyse sont présentés dans ce document: la sélection du signal et son efficacité, l'estimation du bruit de fond, les systématiques associées à la mesure, ainsi que la méthode statistique employée pour l'extraction de la section efficace. La section efficace du processus ZZ sur couche de masse a été mesurée à 6.98±0.41(stat.)±0.36(syst.)±0.20(lumi) pb. La section efficace pour chaque canal a été aussi mesurée dans une volume cinématique ``restreint'', proche du volume reconstruit. Toutes les mesures obtenues sont en accord avec les prédictions theoriques. L'auto-interaction des bosons neutres est interdite dans le Modèle Standard. Si des couplages à trois bosons sont observés, ceux-ci indiqueront donc la présence d'une nouvelle physique. Des observables sensibles à la présence des couplages anormaux ont été examinées. L'impulsion transverse du boson le plus énergétique s'est avérée une des plus sensibles, et elle a été donc utilisée pour l'extraction des limites à 95% CL sur les couplages anormaux. Toutes les limites obtenues sont compatibles avec le Modèle Standard. La connaissance du champ magnétique toroïdal dans le détecteur ATLAS est essentielle pour l'estimation précise de la masse des particules. Une étude sur les senseurs utilisés pour la construction de la carte de champ du détecteur ATLAS a montré que 97% des senseurs sont fiables. La carte de champ existante a été examinée, et malgré l'observation d'anomalies, celles-ci ne sont pas susceptibles d'affecter la détermination de l'impulsion des muons, ni donc de l'estimation de la masse du boson de Higgs.Elementary particles and their interactions are described by the Standard Model. Even successful, there are still some unanswered questions which need to be addressed. In this work, the ZZ Standard Model process was studied in the leptonic decay channel. The data used were collected by the ATLAS detector during 2012 and correspond to an integrated luminosity of 20 fb-1. The center of mass energy was 8 TeV. All the analysis elements, such as the signal selection and efficiencies, the background estimation, the measurement uncertainties and the statistical method employed for the cross section extraction, are discussed in this document. The total ZZ on-shell cross section is measured to be 6.98±0.41(stat.)±0.36(syst.)±0.20(lumi) pb. A measurement of the on-shell ``fiducial'' cross section, defined in a volume close to the reconstructed one, was also performed for each decay channel. Both total and fiducial measurements are in agreement, within uncertainties, with the SM predictions. The neutral boson-self interactions are forbidden in the SM. Therefore, if triple gauge boson couplings are observed, they will indirectly point to the existence of new physics. Observables sensitive to the presence of anomalous triple gauge couplings, along with the optimal binning were investigated. The traverse momentum of the most energetic boson was among the most sensitive observables, and it was thus used in order to extract 95% CL limits on the anomalous coupling parameters. All observed limits are found to be compatible with the SM expectations. In the framework of this thesis a performance study was conducted. In order to increase particles mass measurement precision, the accurate knowledge of the toroidal magnetic field inside the detector is essential. The sensors used for the production of the ATLAS toroidal magnetic field map were studied, and it was found that more than 97% of these sensors are reliable. The existing magnetic field map was probed, and even though inaccuracies were observed, they are not expected to impact muon momentum estimation and thus not to bias the Higgs boson mass measurement

Search for Scalar Diphoton Resonances in the Mass Range 65−60065-600 GeV with the ATLAS Detector in pppp Collision Data at s\sqrt{s} = 8 TeVTeV

A search for scalar particles decaying via narrow resonances into two photons in the mass range 65–600 GeV is performed using $20.3\text{}\text{}{\mathrm{fb}}^{-1}$ of $\sqrt{s}=8\text{}\text{}\mathrm{TeV}$ $pp$ collision data collected with the ATLAS detector at the Large Hadron Collider. The recently discovered Higgs boson is treated as a background. No significant evidence for an additional signal is observed. The results are presented as limits at the 95% confidence level on the production cross section of a scalar boson times branching ratio into two photons, in a fiducial volume where the reconstruction efficiency is approximately independent of the event topology. The upper limits set extend over a considerably wider mass range than previous searches

Search for Higgs and ZZ Boson Decays to J/ψγJ/\psi\gamma and Υ(nS)γ\Upsilon(nS)\gamma with the ATLAS Detector

A search for the decays of the Higgs and $Z$ bosons to $J/\psi\gamma$ and $\Upsilon(nS)\gamma$ ($n=1,2,3$) is performed with $pp$ collision data samples corresponding to integrated luminosities of up to $20.3\mathrm{fb}^{-1}$ collected at $\sqrt{s}=8\mathrm{TeV}$ with the ATLAS detector at the CERN Large Hadron Collider. No significant excess of events is observed above expected backgrounds and 95% CL upper limits are placed on the branching fractions. In the $J/\psi\gamma$ final state the limits are $1.5\times10^{-3}$ and $2.6\times10^{-6}$ for the Higgs and $Z$ bosons, respectively, while in the $\Upsilon(1S,2S,3S)\,\gamma$ final states the limits are $(1.3,1.9,1.3)\times10^{-3}$ and $(3.4,6.5,5.4)\times10^{-6}$, respectively

Measurements of the Total and Differential Higgs Boson Production Cross Sections Combining the H??????? and H???ZZ*???4??? Decay Channels at s\sqrt{s}=8??????TeV with the ATLAS Detector

Measurements of the total and differential cross sections of Higgs boson production are performed using 20.3~fb$^{-1}$ of $pp$ collisions produced by the Large Hadron Collider at a center-of-mass energy of $\sqrt{s} = 8$ TeV and recorded by the ATLAS detector. Cross sections are obtained from measured $H \rightarrow \gamma \gamma$ and $H \rightarrow ZZ ^{*}\rightarrow 4\ell$ event yields, which are combined accounting for detector efficiencies, fiducial acceptances and branching fractions. Differential cross sections are reported as a function of Higgs boson transverse momentum, Higgs boson rapidity, number of jets in the event, and transverse momentum of the leading jet. The total production cross section is determined to be $\sigma_{pp \to H} = 33.0 \pm 5.3 \, ({\rm stat}) \pm 1.6 \, ({\rm sys}) \mathrm{pb}$. The measurements are compared to state-of-the-art predictions.Measurements of the total and differential cross sections of Higgs boson production are performed using 20.3  fb-1 of pp collisions produced by the Large Hadron Collider at a center-of-mass energy of s=8  TeV and recorded by the ATLAS detector. Cross sections are obtained from measured H→γγ and H→ZZ*→4ℓ event yields, which are combined accounting for detector efficiencies, fiducial acceptances, and branching fractions. Differential cross sections are reported as a function of Higgs boson transverse momentum, Higgs boson rapidity, number of jets in the event, and transverse momentum of the leading jet. The total production cross section is determined to be σpp→H=33.0±5.3 (stat)±1.6 (syst)  pb. The measurements are compared to state-of-the-art predictions.Measurements of the total and differential cross sections of Higgs boson production are performed using 20.3 fb$^{-1}$ of $pp$ collisions produced by the Large Hadron Collider at a center-of-mass energy of $\sqrt{s} = 8$ TeV and recorded by the ATLAS detector. Cross sections are obtained from measured $H \rightarrow \gamma \gamma$ and $H \rightarrow ZZ ^{*}\rightarrow 4\ell$ event yields, which are combined accounting for detector efficiencies, fiducial acceptances and branching fractions. Differential cross sections are reported as a function of Higgs boson transverse momentum, Higgs boson rapidity, number of jets in the event, and transverse momentum of the leading jet. The total production cross section is determined to be $\sigma_{pp \to H} = 33.0 \pm 5.3 \, ({\rm stat}) \pm 1.6 \, ({\rm sys}) \mathrm{pb}$. The measurements are compared to state-of-the-art predictions