On the road to Supersymmetry with ATLAS

This thesis is concerned with physics performance of the ATLAS experiment at the LHC, and can roughly be divided into two parts. The first part has to do with the discovery of supersymmetry in events with one lepton, specifically one muon. Chapter 4 describes a data-driven method to estimate the Standard Model backgrounds to supersymmetry searches, describing the techniques and possible results using simulated data. Due to the delay in the LHC start-up, it was not possible to reproduce this study on collision data, on the time scale of this thesis. However it was possible and very exciting to take part in studies with the very first data coming out of ATLAS, since the LHC started colliding protons at 7 TeV collision energy from march 2010. In Chapter 5 the inclusive muon spectrum is studied and compared to simulation. The focus lies on the composition of muons, distinguishing muons coming from pion and kaon decays inside the detector, from the muons coming from the interaction point. First the results based on the very first single muon data are described, while in the second part of the chapter we extend the composition measurement to di-muon events, showing results that include among others the known J/ψ and Z boson resonances. The last chapter, Chapter 3, is concerned with the period of time just before the start of collisions, when the ATLAS detector was commissioned using cosmic rays. In there we focus on the precision chambers of the Muon Spectrometer, which were retrofitted with specialized twin tube boards, to measure not only the precision coordinate but the orthogonal coordinate (in the plane of the chamber) as well. As the LHC and ATLAS embark on a campaign to acquire a large dataset of a few fb−1 in the year 2011, all eyes are focused on the results the scientists at CERN will be publishing, as it is often said nowadays that the time of theoretical predictions should be over and the time for observations has come again.