Abstract

A programme of Higgs boson characterisation studies is already well underway at the LHC experiments but, currently, one of the least understood aspects of its behaviour is how it couples to the heavy Standard Model fermions, including the top quark. In the SM, the coupling of fermions to the Higgs boson is proportional to the fermion mass and so accurate measurements of these Yukawa couplings is crucial. Any deviation from the predicted coupling strengths would be a powerful indication of new physics beyond the SM, with far-reaching consequences for our understanding of physics at large scales. Given its particularly large mass, the top Yukawa coupling is of special interest. But it is precisely its large mass which makes the top quark coupling to the Higgs boson the most difficult to pin down experimentally. A direct measurement of the top quark Yukawa coupling is possible through Higgs boson production in association with a top quark pair (ttH). In this seminar, the ATLAS ttH analysis at cm energy 13 TeV is presented.