Search for new phenomena in events with jets and missing transverse momentum at the high-energy LHC RunII with the ATLAS detector

The work presented in this thesis was carried out in the framework of the ATLAS Experiment at the LHC. It is centered on the search for Supersymmetry, an extension of the Standard Model that predicts the existence of new particles. Specifically, the main topic is the search for the supersymmetric partner of the top quark. The search is performed using proton-proton collisions delivered by the LHC and recorded by the ATLAS Experiment during 2015 and 2016. A profile likelihood fit performed on a number of signal and control regions is used to interpret the data. The results show good agreement with the Standard Model predictions, and 95% CL limits are set on the visible cross section of any new physics phenomena and on the masses of the supersymmetric particles involved in the specific models considered. The results improve the limits set with previous searches by the ATLAS and CMS collaborations.