Search for the $t\overline tH$ production in multi-leptonic final states with the ATLAS detector at LHC

Since its discovery in July 2012, it has become mandatory to study the coupling oh the Higgs boson with other Standard Model particles. The associated produciton of Higgs and top-anti-top couples lets us calculate both ferminonic and bosonic couplings. Cut-based analysis that are performed in ATLAS in this field aim to reveal the cleanest signatures of the top and Higgs decays, meaning those containing b-jets and leptons. The thesis shows the results obtained with the data gathered by ATLAS at LHC in 2012 and the preliminary analysis of the 2015 data. The main topic of the thesis revolves around the implementation and optimization of background estimation techniques.