Studies of the ATLAS Muon Spectrometer with Test Beam and Simulated Physics Data

In the ATLAS detector, muon related measurements are achieved by a huge Muon Spectrometer installed at the outermost region of the detector. At the LHC energies, high-pT muons are expected to be measured with a momentum resolution of ∼ 10% at 1 TeV . The main detecting element of the Muon Spectrometer is the Monitored Drift Tube chamber. The reconstruction potential of a BIS type Monitored Drift Tube chamber, in a special setup at the H8 Testbeam experimental area at CERN, is investigated. Data from the BIS muon chamber with both muon and positron beams are taken and the reconstruction of track segments in the chamber is studied. The correlation of the precision coordinate of the reconstructed track segment with the calorimeter cluster barycentre is also studied. In the ATLAS detector, muons lose parts of their energy in the Calorimetric System before reaching the Muon Spectrometer. As the muon energy increases radiative effects start playing a significant role in the energy loss mechanism and increase the probability for a big muon energy loss, often called as catastrophic. The probability for catastrophic energy losses of 350 GeV muons when they pass through the ATLAS calorimeters is studied with H8 testbeam data. Information on catastrophic muon energy losses in the calorimeters and also on the isolation of muons can be retrieved by a direct measurement of the calorimeter response. For this reason, a precise energ y deposition measurement method in the calorimeters is developed. The method enriches the muon object at the AOD anal- ysis level with information on calorimeter isolation and the collection of calorimeter cells associated with the measurement. The method is applied on single muon and t¯t → 4ℓ + X events. Finally, the Z boson pair production through the process pp → ZZ(∗) → ℓℓℓℓ, where ℓ = e or ℓ = μ is of great interest for the LHC physics searches because it constitutes the irreducible background to the observation of the Higgs boson production through the 4 lepton decay. The observation expectations of pp → ZZ → 4ℓ channel with 1 fb−1 of data is investigated and analysis methods on simulated events of signal and t¯t and Zb¯b backgrounds processes are described.