Astrophysical observations implying the existence of Dark Matter and Dark Energy, which are not described by the Standard Model (SM) of particle physics, have led to extensions of the SM predicting new particles that could be directly produced at the Large Hadron Collider (LHC) at CERN. Based on 2015 and 2016 ATLAS proton-proton collision data, this thesis presents searches for the supersymmetric partner of the top quark, for Dark Matter, and for DarkEnergy, in signatures with jets and missing transverse energy.

Muon detection is key to some of the most important LHC physics results, including the discovery of the Higgs boson and the measurement of its properties. The efficiency with which muons can be detected with the ATLAS detector is measured using Z boson decays. The performance of high-precision Monitored Drift Tube muon chambers under background rates similar to the ones expected for the High Luminosity-LHC is studied.

Auteur
Nicolas Köhler passed his undergraduate studies at the University of Konstanz, Germany, spending 5 months at Canada's national particle accelerator centre (TRIUMF) to write his Bachelor thesis. During his Masters studies at the Technical University of Munich, Germany, he specialised in experimental particle physics, completing both his Master and PhD theses at the Max Planck Institute for Physics. His doctoral degree, granted "with highest distinction" in August 2018, was recognised as being an outstanding contribution to the ATLAS collaboration in the context of a PhD thesis. At present, he is a fellow at the European Organisation for Nuclear Research (CERN).

Contenu
Introduction.- The theory of elementary particle physics.- The experimental setup.- Performance of muon reconstruction and identication.- Searches for new particles decaying into jets and missing transverse energy.- Summary.- Appendix.- Bibliography.