Search for a CP-odd Higgs boson decaying into a heavy CP-even Higgs boson and a Z boson in the ⁺⁻tt̄ and ν ν̄bb̄ final states using 140 fb−1 of data collected with the ATLAS detector

A bstract A search for a heavy CP-odd Higgs boson, A , decaying into a Z boson and a heavy CP-even Higgs boson, H , is presented. It uses the full LHC Run 2 dataset of pp collisions at √s s = 13 TeV collected with the ATLAS detector, corresponding to an integrated luminosity of 140 fb − 1 . The search for A → ZH is performed in the ⁺⁻tt̄ ℓ + ℓ − t t ¯ and ν ν̄bb̄ ν ν ¯ b b ¯ final states and surpasses the reach of previous searches in different final states in the region with m H > 350 GeV and m A > 800 GeV. No significant deviation from the Standard Model expectation is found. Upper limits are placed on the production cross-section times the decay branching ratios. Limits with less model dependence are also presented as functions of the reconstructed m ( tt̄ t t ¯ ) and m ( bb̄ b b ¯ ) distributions in the ⁺⁻tt̄ ℓ + ℓ − t t ¯ and ν ν̄bb̄ ν ν ¯ b b ¯ channels, respectively. In addition, the results are interpreted in the context of two-Higgs-doublet models.