Sensitivity studies for left-right symmetric model heavy neutrinos search with the ATLAS experiment at LHC

Within the Standard Model of particle physics, neutrinos are massless. However, the experimental observation of flavour oscillations suggests otherwise, motivating the search for Beyond the Standard Model extensions. Among these, Seesaw mechanisms offer a natural explanation for the lightness of neutrino masses, especially when embedded within the Left-Right Symmetric Model. This thesis presents a feasibility study for a search for heavy Majorana neutrinos predicted by this model, based on data collected by the ATLAS detector at CERN. The theoretical framework and the Monte Carlo simulation methods used to model both Standard Model background processes and the Beyond the Standard Model signal are introduced. The study then aims at improving the expected sensitivity of the search targeting the heavy-neutrino decay into a dilepton and multi-jets final state, using proton-proton collision data at centre-of-mass energy √s = 13 TeV, corresponding to 140 fb−1 integrated luminosity collected during LHC Run 2. The signal Monte Carlo model is validated at truth-level, alternative selection strategies are developed and their efficiency is quantified. Finally, the expected sensitivity is estimated through a statistical fit and compared to the baseline analysis approach.