Higgs characterisation at NLO in QCD: CP properties of the top-quark Yukawa interaction

TL;DR

This paper investigates the CP properties of the top-quark Yukawa interaction at the LHC by analyzing Higgs production processes, incorporating NLO QCD corrections and parton-shower effects to improve the precision of CP-sensitive observable measurements.

Contribution

The study provides the first detailed analysis of CP-sensitive observables at NLO in QCD, including parton-shower effects, for probing the CP nature of the top-Higgs interaction.

Findings

NLO corrections significantly reduce theoretical uncertainties.

Di-jet correlations in Higgs plus two jets are sensitive to CP properties.

Top-quark decay product correlations can probe CP nature effectively.

Abstract

At the LHC the CP properties of the top-quark Yukawa interaction can be probed through Higgs production in gluon fusion or in association with top quarks. We consider the possibility for both CP-even and CP-odd couplings to the top quark to be present, and study CP-sensitive observables at next-to-leading order (NLO) in QCD, including parton-shower effects. We show that the inclusion of NLO corrections sizeably reduces the theoretical uncertainties, and confirm that di-jet correlations in $H+2$ jet production through gluon fusion and correlations of the top-quark decay products in $t\bar tH$ production can provide sensitive probes of the CP nature of the Higgs interactions.