Angles on CP-violation in Higgs boson interactions

TL;DR

This paper investigates CP-violation in Higgs interactions using angular measurements, interpreting results within the Standard Model Effective Field Theory, and suggests methods to improve constraints at the LHC.

Contribution

It demonstrates how to constrain CP-violating operators in Higgs interactions using angular observables and phase-space effects at the LHC.

Findings

Current measurements do not distinguish CP-violating operators effectively.

Additional observables can improve constraints on CP-violation.

Perturbative constraints are achievable with about 100/fb luminosity.

Abstract

CP-violation in the Higgs sector remains a possible source of the baryon asymmetry of the universe. Recent differential measurements of signed angular distributions in Higgs boson production provide a general experimental probe of the CP structure of Higgs boson interactions. We interpret these measurements using the Standard Model Effective Field Theory and show that they do not distinguish the various CP-violating operators that couple the Higgs and gauge fields. However, the constraints can be sharpened by measuring additional CP-sensitive observables and exploiting phase-space-dependent effects. Using these observables, we demonstrate that perturbatively meaningful constraints on CP-violating operators can be obtained at the LHC with luminosities of ${\cal{O}}$(100/fb). Our results provide a roadmap to a global Higgs boson coupling analysis that includes CP-violating effects.