Event-by-event estimate of the energy loss and study of the multiple scattering of muons in ATLAS

The ATLAS Muon Spectrometer is designed to provide efficient and precise stand-alone muon identification and momentum measurement, more than hundred radiation lengths from the interaction point. Thus, the material induced effects upstream the Muon Spectrometer, namely the energy loss and the multiple Coulomb scattering, should be appropriately accounted for during the back-tracking of a muon track to the production vertex. Moreover, the energy loss fluctuations of the muon upstream the Muon Spectrometer could deteriorate the physics performance. In this thesis, the material effects are studied within the context of muon reconstruction. Furthermore, a method to account for the energy loss fluctuations on an event-by-event basis using the calorimeter information is presented. The improvement in the momentum resolution by the significant suppression of the non-Gaussian tails of the energy loss is demonstrated using simulated single muon data. The performance of the method on physics samples with muons in the final state, is also presented.