Improving probes of $hAA$ coupling in the Type-X two Higgs Doublet Model scenario: the crucial role of τ-jet charge identification

The exotic decay modes of the already discovered 125-GeV scalar into a pair of light pseudoscalars is a good probe of those new physics scenarios where such pseudoscalars exist. Searches in the mass region where the pseudoscalar (A) is lighter than 62.5 GeV have yielded null findings so far. No search has yet examined mA > 62.5 GeV where the cross section is suppressed by the off-shell pseudoscalar. We point out a possible enhancement of the sensitivity of probing $hAA$ coupling in the context of a Type-X two Higgs doublet model. We focus on h→ A A(*) → 4τ, and select events with two same-sign τ-jets along with a pair of same-sign leptons. This enables much more effective background elimination than in the erstwhile proposed channels. Taking two values of the ττ A coupling into account, we obtain limits on the $hAA$ coupling that can be probed at 2σ and 3σ significance, for mA ranging up to 85 GeV. For mA < 62.5 GeV, too, we find the probe through our suggested channel exhibits considerable improvement upon the usual 2μ 2τ-based searches conducted at the LHC. Within this region, achieving the reach of yhAA coupling at 3000 fb⁻¹ luminosity using our strategy would require approximately ~ 3.6× 10⁵ fb⁻¹ luminosity using conventional 2μ 2τ-based searches.