Testing CP Properties of Extra Higgs States at the HL-LHC

TL;DR

This paper explores how to detect CP violation in extra Higgs particles at the HL-LHC, focusing on the Two-Higgs Doublet Model and analyzing decay angular distributions to identify CP admixtures.

Contribution

It proposes a method using angular distributions and machine learning to determine the CP nature of extra Higgs states in the Two-Higgs Doublet Model at the HL-LHC.

Findings

Potential to identify CP violation in Higgs sector at HL-LHC

Use of shape analysis and BDT for signal discrimination

Feasibility within current experimental constraints

Abstract

Extra Higgs states appear in various scenarios beyond the current Standard Model of elementary particles. If discovered at the LHC or future colliders, the question will arise whether CP is violated or conserved in the extended scalar sector. An unambiguous probe of (indirect) CP violation would be the observation that one of the extra Higgs particles is an admixture of a CP-even and a CP-odd state. We discuss the possibility to discover scalar CP violation in this way at the high-luminosity (HL) phase of the LHC. We focus on the Two-Higgs Doublet Model of type I, where we investigate its currently allowed parameter region. Considering a benchmark point that is compatible with the current constraints but within reach of the HL-LHC, we study the prospects of determining the CP property of an extra neutral Higgs state $H$ via the angular distribution of final states in the decay $H \to \tau\bar\tau$. The analysis is performed at the reconstructed level, making use of a Boosted Decision Tree for efficient signal-background separation and a shape analysis for rejecting a purely CP-even or odd nature of $H$.