$t\bar{t}H$ Coupling Measurement with the ATLAS Detector at the LHC

The Higgs boson was discovered on the 4th of July 2012 with a mass around 125 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 ($t\bar{t}H$) at ATLAS is presented in this paper 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 $t\bar{t}H$ 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 $t\bar{t}H$ production process, using 2015-2016 data and combining all $t\bar{t}H$ final states, is $1.8 \pm 0.7$, corresponds to $2.8 \sigma$ ($1.8 \sigma$) observed (expected) significance.