Search for heavy Higgs bosons A/H decaying to a top-quark pair in pp collisions at $\sqrt{s}=8$ TeV with the ATLAS detector

A search for a pseudoscalar (A) or scalar (H) heavy Higgs boson decaying into a top-quark pair ($t\bar{t}$) has been conducted in 20.3 fb$^{−1}$ of data collected by the ATLAS detector at the Large Hadron Collider in proton--proton collisions at a centre-of-mass energy of $\sqrt{s}=8$ TeV. The analysis relies on the invariant mass spectrum of the $t\bar{t}$ pair in final states with an electron or muon, large missing transverse momentum, and at least four jets. Interference effects between the signal process and $gg\rightarrow t\bar{t}$ production in the Standard Model, which heavily distort the signal shape from a single peak to a peak-dip structure, are taken into account. Exclusion limits are derived for two resonance masses (500 and 750 GeV), as a function of the parameter tanβ in Two-Higgs-Doublet Models.