Directly Probing the CP-structure of the Higgs-Top Yukawa at HL-LHC and Future Colliders

Abstract

Constraining the Higgs boson properties is a cornerstone of the LHC program and future colliders. In this Snowmass contribution, we study the potential to directly probe the Higgs-top CP-structure via the $t\bar{t}h$ production at the HL-LHC, 100 TeV FCC and muon colliders. We find the limits on the CP phase ($\hat{I}\pm$) at 95% CL are $|\hat{I}\pm |\lesssim 36^{\circ }$ with dileptonic $t\bar{t}(h\to b\bar{b})$ and $|\hat{I}\pm |\lesssim 25^{\circ }$ with combined $t\bar{t}(h\to {\hat{I}}^3{\hat{I}}^3)$ at the HL-LHC. The 100 TeV FCC brings a significant improvement in sensitivity with $|\hat{I}\pm |\lesssim 3^{\circ }$ for the dileptonic $t\bar{t}(h\to b\bar{b})$, due to the remarkable gain in the signal cross-section and the increased luminosity. At future muon colliders, we find that the bounds with semileptonic $t\bar{t}(h\to b\bar{b})\hat{I}½\bar{\hat{I}}½$ are $|\hat{I}\pm |\lesssim 9^{\circ }$ for 10 TeV and $|\hat{I}\pm |\lesssim 3^{\circ }$ for 30 TeV, respectively.

12 pages, 8 figures, contribution to Snowmass 2021