Reconstructing a light pseudoscalar in the Type-X Two Higgs Doublet Model

TL;DR

This paper explores the potential to detect and reconstruct a light pseudoscalar particle in the 50-60 GeV range within a Type-X Two Higgs Doublet Model, using the decay process of the 125 GeV Higgs boson at the LHC.

Contribution

It demonstrates a feasible method to reconstruct the light pseudoscalar mass via the muon pair channel, enabling discovery with less than 100 fb^{-1} of data at 14 TeV.

Findings

Reconstruction of the pseudoscalar mass is possible using the mu+ mu- decay mode.

The process pp -> h -> AA -> mu+ mu- tau+ tau- can establish the pseudoscalar around 50-60 GeV.

Discovery potential is achievable with about 100 fb^{-1} of integrated luminosity at 14 TeV.

Abstract

We investigate the detectability as well as reconstructibility of a light pseudoscalar particle $A$, of mass in the 50 - 60 GeV range, which is still allowed in a Type-X (lepton-specific) two-Higgs doublet scenario. Such a pseudoscalar can be pair-produced in the decay $h\to AA$ of the 125 GeV scalar $h$. The light pseudoscalar in the aforementioned range, helpful in explaining the muon anomalous magnetic moment, has not only substantial branching ratio in the $\tau^+\tau^-$ channel but also one of about $0.35\%$ in the $\mu^+\mu^-$ final state. We show how to faithfully reconstruct the $A$ mass using the $\mu^+\mu^-$ mode, and establish the existence of a pseudoscalar around 50 - 60 GeV, using the process $pp\to h \to AA\to \mu^+\mu^-\,\tau^+\tau^-$. This is the most reliable way of reconstructing the light $A$ mass, and is possible for an integrated luminosity of about $100~\rm{fb}^{-1}$ or less at 14 TeV, with a statistical significance that amounts to discovery.