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

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, with a statistical significance that amounts to discovery, with a few hundred (or less) fb−1 of integrated luminosity.