Simulation Studies of Digital Filters for the Phase-II Upgrade of the Liquid-Argon Calorimeters of the ATLAS Detector at the High-Luminosity LHC

The Large Hadron Collider and the ATLAS detector are undergoing a comprehensive upgrade split into multiple phases. This effort also affects the liquid argon calorimeters, whose main readout electronics will be replaced completely during the final phase. The electronics consist of an analog and a digital portion: the former amplifies the signal and shapes it to facilitate sampling, the latter executes an energy reconstruction algorithm. Both must be improved during the upgrade so that the detector may accurately reconstruct interesting collision events and efficiently suppress uninteresting ones. In this thesis, simulation studies are presented that optimize both the analog and the digital readout of the Electromagnetic Calorimeters. The simulation is verified using calibration data that has been measured during Run 2 of the ATLAS detector. The influence of several parameters of the analog shaping stage on the energy resolution is analyzed and the utility of an increased signal sampling rate of 80 MHz is investigated. Furthermore, a number of linear and non-linear energy reconstruction algorithms is reviewed and the performance of a selection of them is compared. It is demonstrated that increasing the order of the Optimal Filter, the algorithm currently in use, improves energy resolution by 2 to 3 % in all detector regions. The Wiener filter with forward correction, a non-linear algorithm, gives an improvement of up to 10 % in some regions, but degrades the resolution in others. A link between this behavior and the probability of falsely detected calorimeter hits is shown and possible solutions are discussed.