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

TL;DR

This paper evaluates the potential of future colliders to directly measure the CP-structure of the Higgs-top Yukawa coupling through $t\bar{t}h$ production, showing significant improvements in sensitivity over current limits.

Contribution

It provides projected constraints on the Higgs-top CP-phase at HL-LHC, FCC, and muon colliders, highlighting the enhanced sensitivity of future collider experiments.

Findings

HL-LHC can constrain CP phase to about 25-36 degrees.

FCC at 100 TeV can improve sensitivity to about 3 degrees.

Muon colliders at 10-30 TeV can constrain CP phase to about 3-9 degrees.

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 ($\alpha$) at 95% CL are $|\alpha| \lesssim 36^\circ$ with dileptonic $t\bar t (h\to b\bar b) $ and $|\alpha| \lesssim 25^\circ$ with combined $t\bar t (h\to \gamma\gamma) $ at the HL-LHC. The 100 TeV FCC brings a significant improvement in sensitivity with $|\alpha| \lesssim 3^\circ$ 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 $t\bar t (h\to b\bar b) \nu\bar\nu$ are $|\alpha| \lesssim 9^\circ$ for 10 TeV and $|\alpha| \lesssim 3^\circ$ for 30 TeV, respectively.