Search for a CP-odd Higgs boson decaying into a heavy CP-even Higgs boson and a $Z$ boson in the $\ell^+\ell^- t\bar{t}$ and $\nu\bar{\nu}b\bar{b}$ final states using 140 fb$^{-1}$ of data collected with the ATLAS detector

The ATLAS collaboration
Aad, Georges , Abbott, Braden Keim , Abeling, Kira , Abicht, Nils Julius , Abidi, Haider , Aboulhorma, Asmaa , Abramowicz, Halina , Abreu, Henso , Abulaiti, Yiming , Acharya, Bobby Samir
JHEP 02 (2024) 197, 2024.

Abstract (data abstract)
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 using the full LHC Run 2 dataset of $pp$ collisions at $\sqrt{s}=13$ TeV collected with the ATLAS detector, corresponding to an integrated luminosity of $140$ fb$^{-1}$. The search for $A\to ZH$ is performed in the $\ell^+\ell^- t\bar{t}$ and $\nu\bar{\nu}b\bar{b}$ final states and extends the reach of previous searches into 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 on the production cross-section times the decay branching ratios are set. Limits with a reduced model dependence are also presented as functions of the reconstructed $m(t\bar{t})$ and $m(b\bar{b})$ distributions in the $\ell^+\ell^- t\bar{t}$ and $\nu\bar{\nu}b\bar{b}$ channel, respectively. In addition, an interpretation of the results in the context of two-Higgs-doublet models is given.

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