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Performances du calorimètre électromagnétique et recherche de nouveaux bosons de jauge dans le canal diélectron auprès du détecteur ATLAS

Abstract : 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.
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  • HAL Id : tel-00782463, version 2

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Emmanuel Laisne. Performances du calorimètre électromagnétique et recherche de nouveaux bosons de jauge dans le canal diélectron auprès du détecteur ATLAS. Physique des Hautes Energies - Expérience [hep-ex]. Université de Grenoble, 2012. Français. ⟨NNT : 2012GRENY093⟩. ⟨tel-00782463v2⟩

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