Search for Pair Production of Higgs Bosons in the Four Bottom Quark Final State Using Proton-Proton Collisions at sqrt(s) = 13 TeV with the ATLAS Detector

A search for Higgs boson pair production in the bbbb final state is carried out with up to 36.1 fb-1 of LHC proton–proton collision data collected at sqrt(s) = 13 TeV with the ATLAS detector in 2015 and 2016. Three benchmark signals are studied: a spin-2 graviton decaying into a Higgs boson pair, a scalar resonance decaying into a Higgs boson pair, and Standard Model non-resonant Higgs boson pair production. This thesis presents a search in events with four individually resolved b-tagged jets. Higgs bosons produced with large momenta are reconstructed as single large radius jets with substructure. The analysis of this topology is presented in [197]. The two analyses are statistically combined and upper limits on the production cross section of Higgs boson pairs times branching ratio to bbbb are set in each model. The combined result searches for resonance masses in the range 260-3000 GeV. No significant excess is observed; the largest deviation of data over prediction is found at a mass of 280 GeV, corresponding to 2.3 standard deviations globally. The observed 95% confidence level upper limit on the non-resonant production is 13 times the Standard Model prediction.