Abstract
A study of the charge conjugation and parity (πΆβ’π) properties of the interaction between the Higgs boson and top quarks is presented. Higgs bosons are identified via the diphoton decay channel (π» βπΎβ’πΎ), and their production in association with a top quark pair (π‘β’π») or single top quark (π‘β’π») is studied. The analysis uses 139ββfbβ1 of protonβproton collision data recorded at a center-of-mass energy of βπ =13ββTeV with the ATLAS detector at the Large Hadron Collider. Assuming a πΆβ’π-even coupling, the π‘β’π‘β’π» process is observed with a significance of 5.2 standard deviations. The measured cross section times π» βπΎβ’πΎ branching ratio is 1.64+0.38β0.36β’(stat)+0.17β0.14(sys)ββfb, and the measured rate for π‘β’Β―π‘π» is 1.43+0.33β0.31β’(stat)+0.21β0.15(sys) times the Standard Model expectation. The π‘β’π» production process is not observed and an upper limit on its rate of 12 times the Standard Model expectation is set. A πΆβ’π-mixing angle greater (less) than 43 (β43)Β° is excluded at 95% confidence level.