Constraining the Top Yukawa Coupling in tH Production with the ATLAS Experiment at the LHC

Using the full Run 2 luminosity from the LHC, we can design analyses that are sensitive to the rare tH (single-top Higgs) production process. The tH process is extremely sensitive to the sign of the top quark Yukawa coupling (Yt), providing an excellent opportunity to constrain it. In this talk, I will present a novel analysis in the di-photon decay channel of the Higgs boson, using 139 ifb of data recorded by the ATLAS experiment at sqrt(s)=13 TeV. This analysis uses new Machine Learning techniques to simultaneously optimise the Standard Model tH sensitivity and the exclusion of negative values of Yt. I will discuss the motivation behind the analysis, cover the details of its design, and present the limits on the tH cross-section. The interpretation of the result within the kappa framework shows the importance of this analysis for our understanding of the top quark Yukawa interaction.