A search for third-generation leptoquarks in the non-resonant production with the ATLAS experiment and development of the Level-0 muon trigger for the High Luminosity LHC

Recent observations performed by several high-energy physics experiments have shown anomalies in b-hadron decays, which could be explained by assuming the existence of a particle, the leptoquark, coupled both to leptons and quarks. Such measurements also suggest a preferential coupling to third-generation fermions. In this thesis, a search for third-generation leptoquarks is presented, considering the non-resonant leptoquark production. The non-resonant production is expected to yield high sensitivity from the large interference term between the Standard Model Drell-Yan process and the leptoquark t-channel exchange. The leptoquark search uses the 140 fb−1 of pp collision data collected by the ATLAS detector during the LHC Run 2 and considers di-lepton final state events, with at least one hadronically decaying tau-lepton. Deviations from the Standard Model predictions are looked for in the visible invariant mass spectrum of the di-lepton system, binned in b-jet multiplicity. In the absence of a significant deviation, exclusion limits are determined on the leptoquark coupling for different leptoquark mass values. This thesis also presents a contribution to the upgrade of the ATLAS Muon Spectrometer in preparation for the High-Luminosity LHC. In order to cope with the much harsher conditions of the high-luminosity phase of the LHC, the entire trigger and readout electronics of the Resistive Plate Chamber detectors in the barrel region of the Muon Spectrometer will be replaced and novel FPGA-based boards will be installed. On-detector Data Collector and Transmitter boards will collect the front-end data and transmit them to off-detector Sector Logic boards, which will execute the Level-0 Muon trigger algorithm and the readout logic. In this thesis, the development of the firmwares that will be implemented in the FPGAs of the Data Collector and Transmitter boards and of the barrel Sector Logic boards is presented.