Can a pseudoscalar with a mass of 365 GeV in the 2HDM explain the CMS $t\bar{t}$ excess?

TL;DR

This paper investigates whether a 365 GeV pseudoscalar in 2HDMs can explain the CMS t tbar excess, but finds constraints and recent measurements rule out this explanation in conventional models.

Contribution

The study provides a comprehensive analysis of 2HDM parameter space considering multiple constraints, concluding that conventional 2HDMs cannot account for the CMS t tbar excess.

Findings

Flavor constraints exclude Types II and Y.

Parameter space in Types I and X is ruled out by t tbar Z measurements.

Perturbativity limits Higgs masses below 723 GeV.

Abstract

We analyze the CMS-reported t tbar excess within conventional Two-Higgs-Doublet Models of Types I, II, X, and Y, using the best-fit pseudoscalar parameters MA = 365 GeV, GammaA over MA = 2 percent, and tan beta = 1.28. Applying theoretical and experimental constraints, including stability, unitarity, perturbativity, flavor constraints, and collider bounds, we find that perturbativity limits the charged and heavy neutral Higgs masses to below about 723 GeV. Flavor constraints exclude Types II and Y, while the remaining parameter space in Types I and X is ruled out by recent t tbar Z measurements from ATLAS and CMS. We conclude that conventional Two-Higgs-Doublet Models cannot explain the observed t tbar excess, although toponium effects in the background modeling may modify this conclusion. This contribution is based on the proceedings of the 18th International Workshop on Top Quark Physics (TOP2025).