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Abstract

With the discovery of the 125 GeV Higgs boson, both the measurements of Higgs properties and the searches for new physics with Higgs bosons moved into focus of the physics programme of high energy experiments. The most frequent decay channel of the Higgs boson, the Higgs to bb process, is one of the natural choices to search for anomalous Higgs production. Focusing on this decay channel in boosted topologies, this thesis discusses the improved identification techniques for Higgs boson, and presents two searches using those techniques. The first analysis searches for pair-production of boosted Higgs bosons in the bbbb final state with 36.1 ifb of ATLAS pp data collected in 2015 and 2016 at 13 TeV. The analysis looks for resonances in the invariant mass region of Higgs pairs between 800 GeV and 3000 GeV. The second analysis searches for boosted bbbar pairs produced in association with an additional initial state radiation jet using 80.5 ifb of ATLAS pp data collected in 2015, 2016 and 2017 at 13 TeV. Targeting the dijet invariant mass spectrum below 230 GeV, the analysis searches for new resonances predicted by simplified dark matter models as well as Standard Model boosted Higgs boson production. No indication of new physics observed in both analyses, and the results are used to constrain the phase space for beyond the Standard Model physics.