First ATLAS results on ttH at 13 TeV

To understand the nature of the Higgs boson discovered with the LHC experiments ATLAS and CMS in 2012, it is important to search for the yet unobserved Higgs production and decay modes predicted by the Standard Model (SM) of particle physics. Associated production of the Higgs boson and a top-antitop quark pair (ttH production) is one of the yet unobserved processes, with a unique property that it offers a tree-level access to measuring the Higgs-top Yukawa coupling. With a predicted numerical value close to unity, this coupling plays a pivotal role in the stability of the Higgs potential at high energy scales, and also represents the most promising portal to searches for New Physics through fine deviations from the SM predictions. To maximise the chance to observe the SM ttH production, that makes only 1% of the total Higgs boson production cross-section in proton-proton (pp) collisions at the centre of mass energy of 13 TeV, it is necessary to exploit all accessible and sensitive final states. Due to the richness of the Higgs and top-antitop quark pair phenomenologies, this results in quite a complex landscape of search channels. In this talk, a summary of all ATLAS searches for the ttH production performed with 36.1 fb-1 of LHC pp collisions at 13 TeV will be presented. A combination of all these searches provides a first evidence for the ttH production process.