# Probing the CP nature of the Higgs coupling in $t{\bar t}h$ events at the LHC

## TL;DR

This paper investigates the CP properties of the Higgs coupling to top quarks at the LHC using $t\bar{t}h$ events, exploring angular distributions and asymmetries to distinguish scalar, pseudo-scalar, and mixed CP states.

## Contribution

It introduces new angular observables and asymmetries in $t\bar{t}h$ events to effectively probe the CP nature of the Higgs-top coupling, including mixed CP states.

## Key findings

- Significant differences in angular distributions between CP states.
- Effective separation of scalar and pseudo-scalar components.
- Potential for a global fit of Higgs coupling parameters.

## Abstract

The determination of the CP nature of the Higgs coupling to top quarks is addressed in this paper, using $t{\bar t} h$ events produced in $\sqrt{s} = 13$ TeV proton-proton collisions at the LHC. Dileptonic final states are employed, with two oppositely charged leptons and four jets, corresponding to the decays $t\rightarrow bW^+ \rightarrow b \ell^+\nu_\ell$, $\bar{t}\rightarrow \bar{b}W^- \rightarrow \bar{b} \ell^-\bar{\nu}_\ell$ and $h\rightarrow b\bar{b}$. Pure scalar ($h=H$), pure pseudo-scalar ($h=A$) and CP-violating Higgs boson signal events, generated with MadGraph5_aMC@NLO, are fully reconstructed through a kinematic fit. We furthermore generate samples that have both a CP-even and a CP-odd component in the $t \bar t h$ coupling in order to probe the ratio of the two components. New angular distributions of the decay products, as well as CP angular asymmetries, are explored in order to separate the scalar from the pseudo-scalar components of the Higgs boson and reduce the contribution from the dominant irreducible background, $t{\bar t}b{\bar b}$. Significant differences between the angular distributions and asymmetries are observed, even after the full kinematic fit reconstruction of the events, allowing to define the best observables for a global fit of the Higgs couplings parameters.