Improvement of calorimeter-based muon identification and its application to $H \to ZZ^{(*)}\to 4l$ analysis in the ATLAS experiment

Outermost part of the ATLAS detector, the muon spectrometer, is dedicated for detection of muons and measurement of their properties. However, combining the measurements from other parts of the detector with muon spectrometer measurements improves the performance of reconstruction and identification of muons. A complementary method to these strategies is the identification of muons in the calorimeter, without using the muon spectrometer measurements. Energy deposition of muons in the calorimeter has distinct characteristics, which enables their identification by using the energy loss measurements. This method is especially useful for identification of the muons that are failed to be reconstructed due to their insufficiently low momenta to traverse the full muon spectrometer or even to reach it, or due to traversing low-acceptance regions of the muon spectrometer. One of the calorimeter-based muon identification algorithms has been improved within this thesis work. The performance of the improved algorithm and the results of its application to H → ZZ* → 4l analysis are presented. Also, possible extensions for further improvements are discussed.