Le quark top comme sonde pour la recherche de nouvelle physique au LHC, avec le détecteur ATLAS

The work of this thesis focuses on the search for new physics beyond the Standard Model in the compositeness framework, which postulates strongly coupled sectors at the TeV-scale consisting of exotic particles. Their existence can be tested at the CERN proton-proton collider, the LHC, using the ATLAS detector. The production of an heavy quark, such as the $T_{5/3}$ predicted in those models, can be inferred from an enhancement of the cross-section of a given signature. Some final states, such as the one studied in this thesis involving 2 same-sign leptons, are very rare and have an excellent sensitivity. Searches for $T_{5/3}$ production at the LHC using 8 and 13 TeV ATLAS data are presented. A small excess is seen at 8 TeV. Preliminary results of the 13 TeV analysis are presented and do not show any excess. The inferior limit put on the $T_{5/3}$ mass is 745 GeV at 8 TeV and 990~GeV at 13 TeV. Composite models include also heavy bosons such as top-philic $Z'$ coupled only to the top quark whose production in association to a top quark pair gives a final state similar to those from 4 tops events. A phenomenological study on the discovery potential of those exotic ($Z'$ and effective theory) or standard ($t\bar{t}t\bar{t}$) processes at 13 and 14 TeV is done and gives the minimal luminosities needed to observe deviations from the Standard Model. An instrumental study for the conception of the new LTDB card, part of the electromagnetic calorimeter's level 1 trigger system is described in the context of the ATLAS upgrade program.