Search for Higgs boson pair production with the ATLAS detector at the LHCNovak, Jakob (Avtor) Kerševan, Borut Paul (Mentor) Gorišek, Andrej (Komentor) ATLASmachine learningHiggs pair productionsingle-leptonCERNneural networksHiggs self-interactiontwo b-jetsLHC Run 2classification problemBSM scalar resonancemissing transverse momentumThe thesis presents the search for Higgs boson pair production where one Higgs boson decays via $H\to bb$ and the other Higgs boson decays via $H/S \to WW^* \to \ell\nu qq$ (where $\ell$ is either an electron or a muon). The latter can be Standard Model Higgs boson or beyond Standard Model Higgs boson with same couplings but different mass. Analysed data consists of pp collisions at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider. Full Run 2 dataset corresponding to integrated luminosity of 140.1 fb$^{-1}$ is used. Machine learning approach is adopted for selection of events matching the signal topology. No statistically significant evidence of a signal is observed and corresponding upper limits on the production cross-section for $HH$ and $SH$ production are derived.20242024-05-01 07:15:05Doktorsko delo/naloga156036sl