Exploring the low $$\tan \beta $$ region of two Higgs doublet models at the LHC

Current interpretations of the LHC results on two Higgs doublet models (2HDM) underestimate the sensitivity due to neglecting higher order effects. In this work, we revisit the impact of these effects using the current cross-section times branching ratio limits of the $$A\rightarrow hZ, H \rightarrow VV$$ A → h Z , H → V V and $$H\rightarrow hh$$ H → h h channels. With a degenerate heavy Higgs mass $$m_\varPhi $$ m Φ , we find that the LHC searches gain sensitivity to the small $$\tan \beta $$ tan β region after including loop corrections, even close to $$\cos (\beta -\alpha )=0$$ cos ( β - α ) = 0 which is not reachable at tree level for all types of 2HDM. For a benchmark point with $$m_\varPhi =300$$ m Φ = 300 GeV, $$\tan \beta <1.8(1.2)$$ tan β < 1.8 ( 1.2 ) can be probed for the Type-I(II) 2HDM model for $$\cos (\beta -\alpha )=0$$ cos ( β - α ) = 0 . When the deviation from $$\cos (\beta -\alpha )=0$$ cos ( β - α ) = 0 is larger, the region for which current searches have exclusion potential becomes larger.