Muon tracks through ATLAS

What is mass and why is there mass? The answer to these philosophical questions can not be given in this thesis, but they are handled in a different form. Namely, how fundamental is mass and how can mass be measured. In this thesis, computer software is analysed that is used for the reconstruction of muon tracks in the ATLAS detector, which is part of the LHC experiment. With the detailed knowledge of the software, in particular MuFit, it becomes possible to study high energy, particle physics. The analysis concentrates on the so-called golden decay channel where a Higgs boson decays into four muons. This decay gives a well recognizable signal in the muon spectrometer though four muon background events exist that lead to comparable signals. Precise characteristics are infered when subjecting the signal to invariant mass cuts as to reduce the number of background events below the number of genuine Higgs events. Using a proper definition of significance, the conclusion is that the ATLAS detector will be well able to prove the existence of the Higgs signal within a few years after the start of the experiment in 2007. If it turns out that the Higgs particle does not exist, so that the Standard Model fails to be valid, then the studies in this thesis still remain to be important for the discovery of new, unexpected particles.