Performance du calorimètre à argon liquide et recherche du boson de Higgs dans son canal de désintégration H->ZZ*->4l avec l'expérience ATLAS auprès du LHC.

Abstract : The work presented in this thesis within the ATLAS collaboration was performed in the context of the discovery of a new particle at the LHC in the search for the Standard Model Higgs boson. My contribution to the Higgs boson search is focused in the H->ZZ*->4lchannel at different level, from the data taking to the physics analysis. After a theoretical introduction, the LHC and the ATLAS detector are presented as well as their performance during the 2011 and 2012 runs. A particular consideration is given to the liquid argon calorimeters and to the data quality assessment of this system. The validation of the data recorded during non-nominal high voltage conditions is presented. This study allowed to recover 2% of the data collected available for physics analyses. This has a direct impact on the H->ZZ*->4l channel were the number of signal events expected is very low. In order to optimize the acceptance of the four electrons decay channel, novel electron reconstruction algorithms were introducted in 2012. The measurement of their efficiency is presented. The efficiency gain reaching 7% for low transverse energy electrons (15ZZ*->4l analysis presented using the data recorded in 2012. The reducible background estimation methods in the channels containing electrons in the final state that were of primary importance after the discovery are detailed. Finally, the measurement of the new boson properties are presented based on the 2011 and the 2012 recorded data.
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Élodie Tiouchichine. Performance du calorimètre à argon liquide et recherche du boson de Higgs dans son canal de désintégration H->ZZ*->4l avec l'expérience ATLAS auprès du LHC.. Physique [physics]. Aix-Marseille Université, 2014. Français. ⟨tel-01129989⟩

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