Probing the low mass pseudoscalar in flipped Two Higgs Doublet Model

The phenomenology of the flipped two-Higgs-doublet model (2HDM) is relatively less explored so far, as compared to the other, commonly discussed, types. It is found that this scenario, like several others, admits of a light neutral pseudoscalar A in the mass range 20 - 60 GeV, consistently with all current experimental data and theoretical constraints. However, the fact that such a pseudoscalar decays overwhelmingly into a bb̄ pair makes its identification at the Large Hadron Collider (LHC) a challenging task. After identifying the region of the flipped 2HDM parameter space yielding a light pseudoscalar, we identify a useful search channel in the process pp → A Z(Z*) → bb̄ ⁺ ⁻. A cut-based analysis, followed by one based on Boosted Decision Trees, shows that the light-A scenario in flipped 2HDM should be detectable with rather high statistical significance at the high-luminosity LHC run, even after including systematic uncertainties. Furthermore, part of the parameter space, especially around mA = 30 - 40 GeV is amenable to detection at the discovery level within Run-2 itself.