This poster presents the search for CP-violation in the top Yukawa coupling using ttH and tH production modes in the diphoton decay channel (H → γγ). The analysis is based on the 139 fb−1 of proton-proton colli- sion data at center-of-mass energy √s = 13 TeV recorded with the ATLAS detector at the Large Hadron Collider. Two separate sets of selections are introduced to capture the full hadronic and leptonic decay of the tt sys- tem each. This search is performed using a simultaneous fit to the mγγ distribution in analysis categories defined to enhance signal over continuum background and also to separate the CP even and CP odd signal hypotheses. The expected significance for ttH signal is 4.4σ. The observed significance is 5.2σ. The expected and observed limits for tH production are 11.7× and 11.6× the Standard Model prediction, respectively. Two-dimensional con- tours of κt cos(α) and κt sin(α) are derived. A CP-mixing angle above 43◦ (63◦ expected) is excluded at 95% confidence level, and CP-odd hypothesis is rejected at the 3.9σ level.
|Collaboration / Activity||ATLAS|