Higgs from top to bottom Discovery of the Higgs boson coupling to top quarks with the ATLAS detector

In the Standard Model (SM) of particle physics, it is expected that the Higgs boson as a scalar spin-0 particle gives mass to all other elementary particles.
In addition, the coupling to the top quark, as the heaviest elementary particle, is expected to be of order unity.
Proton--proton collision data at a center of mass energy of 13 TeV collected by the ATLAS experiment during Run 2 of the Large Hadron Collider is used to study the interaction between the Higgs boson and the top quark.
Data of up to 79.8 fb^-1 in various Higgs boson decay modes is analyzed to study Higgs boson production in association with a pair of top quarks (ttH) and probe the SM expectation.
This thesis focuses on Higgs decays to bottom quarks and faces the challenges inherent to this decay mode such as limited amount of Monte Carlo statistics and limited understanding of the background modeling.
In this thesis, the collected data is used to establish the Higgs boson-top quark coupling by combining analyses targeting different Higgs boson decay modes, employing cutting edge statistical methods.
The extracted cross-section ratio with respect to the SM prediction of the ttH process is measured to be 1.32 (+0.28 -0.26) in agreement with the SM expectation.
This constitutes a discovery with a significance of 5.8 standard deviations and establishes the coupling between the Higgs boson and the top quark.