LHC signatures of a light pseudoscalar in a flipped two-Higgs scenario: the usefulness of boosted $b{\bar b}$ pairs

TL;DR

This paper explores detecting a light pseudoscalar Higgs in a flipped 2HDM at the LHC using boosted $b\bar{b}$ pairs and machine learning techniques, achieving significant potential discovery signals.

Contribution

It introduces a novel analysis strategy employing boosted decision trees and jet tagging to identify light pseudoscalars in a challenging parameter space.

Findings

Potential for 5-10 sigma significance with 3 ab$^{-1}$ luminosity.

Boosted $b\bar{b}$-pair tagging enhances detection prospects.

Analysis accounts for backgrounds and fake signals.

Abstract

Similar to some other two-Higgs doublet models (2HDM), the flipped 2HDM admits of a light pseudoscalar physical state whose mass can be well below 50 GeV. The fact that the pseudoscalar decays dominantly into a $b{\bar b}$ pair makes its identification at the Large Hadron Collider (LHC) difficult. Moreover, the regions of the parameter space corresponding to a light pseudoscalar tend to jeopardize perturbativity at a rather low scale. One possibility that ameliorates this problem is to postulate that the light physical state has the admixture of an SU(2) singlet field. In such a situation, however, the production mode of the pseudoscalar along with a $Z$ (which provides a useful tag) gets suppressed. We have here chosen to fall back on the QCD-driven final state, namely, one or two jets, together with an energetic squeezed $b{\bar b}$-pair. We utilize boosted di-b-jet tagging techniques and a strategy based on boosted decision trees (BDT) to analyze the signals, considering all backgrounds and likely fakes (mostly from charmed quarks). We find that, including 10\% systematics, one can expect signal significance of 5-10$\sigma$ with an integrated luminosity of 3 $ab^{-1}$.