Development of a new reconstruction and classification method for Tau leptons and its application in the ATLAS detector at the LHC

This thesis documents the development of a new reconstruction and classification method for tau leptons in the ATLAS detector at the LHC. It also presents a possible application of the new reconstruction and classification method. The new reconstruction method follows the energy flow approach and thus aims at reconstructing every decay product of the tau. This method utilises the different subdetectors of ATLAS, by combining their measurements, which allows to reconstruct the charged and neutral pions separately. The new classification method combines the result of the new reconstruction method with kinematics of the tau decay. By calculating kinematic tau variables, for instance the angles between the tau decay products, additional information about the decay is made available. Following this approach, it is possible to reconstruct the decay mode and to improve the energy and spatial resolution of the tau. A possible application of the new tau reconstruction and classification is the measurement of the mean tau polarisation. In a simulation-based analysis, it is shown that the new reconstruction and classification method allows for such measurements.