Reconstructing a light pseudoscalar in the Type-X two Higgs doublet model

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→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 τ⁺τ⁻ channel but also one of about 0.35% in the μ⁺μ⁻ final state. We show how to faithfully reconstruct the A mass using the μ⁺μ⁻ mode, and establish the existence of a pseudoscalar around 50 - 60 GeV, using the process pp→h→AA→μ⁺μ⁻τ⁺τ⁻. This is the most reliable way of reconstructing the light A mass, and is possible for an integrated luminosity of about 100 fb⁻ or less at 14 TeV, with a statistical significance that amounts to discovery.