Angles on CP-violation in Higgs boson interactions

Florian U Bernlochner,Christoph Englert,Chris Hays,Kristin Lohwasser,Hannes Mildner,Andrew Pilkington,Darren D Price,Michael Spannowsky

doi:10.1016/j.physletb.2019.01.043

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 O(100/fb). Our results provide a roadmap to a global Higgs boson coupling analysis that includes CP-violating effects.

Highlights

The matter–antimatter asymmetry of the Universe provides one of the primary motivations to study extensions of the Standard Model of Particle Physics (SM)
Interpreting the results in the Standard Model Effective Field Theory (SMEFT), we find that the current data cannot distinguish between different sources of CP violation, with three blind directions when one considers the four CP-odd operators that cause anomalous Higgs boson interactions with weak bosons or gluons
A better understanding of the Higgs-boson properties remains a crucial part of the Large Hadron Collider (LHC) phenomenology programme, offering a wealth of opportunities to connect the electroweak scale with other well-established features of beyond-the-SM physics

Summary

Introduction

The matter–antimatter asymmetry of the Universe provides one of the primary motivations to study extensions of the Standard Model of Particle Physics (SM). The current constraints on the Higgs boson interactions provided by the ATLAS and CMS experiments at the Large Hadron Collider (LHC) still allow coupling deviations of 10% (or larger) from the SM predictions [17,18,19,20,21,22,23]. As such, they are too loosely constrained to provide a fine-grained picture of electroweak symmetry breaking.

Theoretical framework

Framework and fitting

Results with existing measurements

Enhancing the sensitivity to CP-violation in the Higgs sector

Conclusions