ttH Coupling Measurement with the ATLAS Detector at the LHC

The Higgs boson is discovered on the 4th of July 2012 with a mass around 125 $\text{GeV}/c^2$ by ATLAS and CMS experiments at LHC. Determining the Higgs properties (production and decay modes, couplings,...) is an important part of the high-energy physics programme in this decade. A search for the Higgs boson production in association with a top quark pair (ttH) at ATLAS is presented in this talk at an unexplored center-of-mass energy of 13 TeV, which could allow a first direct measurement of the top quark Yukawa coupling and could reveal new physics. The ttH analysis in ATLAS is divided into 3 channels according to the Higgs decay modes: $H \rightarrow$ Hadrons, $H \rightarrow$ Leptons and $H \rightarrow$ Photons. The best-fit value of the ratio of observed and Standard Model cross sections of ttH production process, using 2015-2016 data and combining all ttH final states, is 1.8 $\pm$ 0.7, corresponds to 2.8 $\sigma$ (1.8 $\sigma$) observed (expected) significance.