A study of Higgs $\boldsymbol{CP}$ properties using the Higgs Characterization Model and top associated production

TL;DR

This paper investigates the $CP$ properties of the Higgs boson coupling to top quarks using simulations of proton-proton collisions, analyzing different $CP$ eigenstates and their experimental signatures with the ATLAS detector conditions.

Contribution

It applies the Higgs Characterization model to simulate and analyze $CP$ properties in top-associated Higgs production, providing a framework for future experimental tests.

Findings

Most $CP$ sensitive variables include transverse momenta of Higgs, leptons, and photons.

Hardening of these variables indicates a transition towards $CP$ odd Higgs couplings.

Current data cannot conclusively determine the Higgs $CP$ eigenstate.

Abstract

This study utilises the Higgs Characterization model to investigate the $CP$ properties of the Higgs coupling to the top quark using the $tH$ and $t\bar{t}H$ generation processes. This is done via simulations of proton-proton collisions with ATLAS detector conditions, which are calculated for seven different $CP$ eigenstates using MadGraph5_aMC@NLO. Three orthogonal categories of cuts are subsequently implemented to find the cut efficiencies, which are used in conjunction with the cross-section to find the signal strength. Comparing the signal strength with experimental results shows that one cannot yet conclusively rule out any Higgs $CP$ eigenstates. Analysing histograms showed that the most $CP$ sensitive variables were the transverse momenta of the Higgs, leptons and photons, which showed a hardening as the Higgs coupling became $CP$ odd.