Probing a light CP-odd scalar in di-top-associated production at the LHC

TL;DR

This paper explores the LHC's potential to detect light CP-odd scalars in di-top production, using jet substructure techniques, and relates findings to various theoretical models, addressing their detectability and constraints.

Contribution

It introduces a novel analysis method for CP-odd scalars at the LHC and connects experimental limits to theoretical models like 2HDMs and NMSSM.

Findings

LHC can set tight limits on CP-odd scalars related to the Galactic Centre excess.

Direct detection of light CP-odd scalars from NMSSM remains difficult.

Jet substructure techniques improve sensitivity in di-top-associated production searches.

Abstract

CP-odd scalars are an integral part of many extensions of the Standard Model. Recently, electroweak-scale pseudoscalars have received increased attention in explaining the diffuse gamma-ray excess from the Galactic Centre. Elusive due to absence of direct couplings to gauge bosons, these particles receive only weak constraints from direct searches at LEP or searches performed during the first LHC runs. We investigate the LHC's sensitivity in observing a CP-odd scalar in di-top associated production in the mass range $20 \leq m_A \leq 100$ GeV using jet substructure based reconstruction techniques. We parametrise the scalar's interactions using a simplified model approach and relate the obtained upper limits to couplings within type-I and type-II 2HDMs as well as the NMSSM. We find that in di-top-associated production, experiments at the LHC can set tight limits on CP-odd scalars that fit the Galactic Centre excess. However, direct sensitivity to light CP-odd scalars from the NMSSM proves to remain challenging.