Probing the Top-Higgs Yukawa CP Structure in dileptonic $t \bar t h$ with $M_2$-Assisted Reconstruction

TL;DR

This paper investigates the potential to measure the CP-structure of the Higgs-top interaction at the LHC using dileptonic $t\bar{t}h$ events, introducing a robust reconstruction method that enhances sensitivity to CP-violation.

Contribution

The study introduces a novel $M_2$-based reconstruction technique for dileptonic $t\bar{t}h$ events, improving CP-sensitivity and background suppression in Higgs-top CP-phase measurements.

Findings

Higgs-top CP-phase can be probed up to $\cos\alpha<0.7$ at the HL-LHC.

The $M_2$-based method is robust against shower, hadronization, and detector effects.

Large CP-sensitivity observed through combined lab and $t\bar{t}$ rest frame observables.

Abstract

Constraining the Higgs boson properties is a cornerstone of the LHC program. We study the potential to directly probe the Higgs-top CP-structure via the $t\bar{t}h$ channel at the LHC with the Higgs boson decaying to a bottom pair and top-quarks in the dileptonic mode. We show that a combination of laboratory and $t\bar{t}$ rest frame observables display large CP-sensitivity, exploring the spin correlations in the top decays. To efficiently reconstruct our final state, we present a method based on simple mass minimization and prove its robustness to shower, hadronization and detector effects. In addition, the mass reconstruction works as an extra relevant handle for background suppression. Based on our results, we demonstrate that the Higgs-top CP-phase $(\alpha)$ can be probed up to $\cos\alpha< 0.7$ at the high luminosity LHC.