Search for a heavy Higgs boson decaying into a Z boson and another heavy Higgs boson in the $\ell \ell bb$ and $\ell \ell WW$ final states in pp collisions at $\sqrt{s}=13$ $\text {TeV}$ with the ATLAS detector

Abstract A search for a heavy neutral Higgs boson, A , decaying into a Z boson and another heavy Higgs boson, H , is performed using a data sample corresponding to an integrated luminosity of 139 fb $^{-1}$ - 1 from proton–proton collisions at $\sqrt{s} = 13$ s = 13   $\text {TeV}$ TeV recorded by the ATLAS detector at the LHC. The search considers the Z boson decaying into electrons or muons and the H boson into a pair of b -quarks or W bosons. The mass range considered is 230–800  $\text {GeV}$ GeV for the A boson and 130–700  $\text {GeV}$ GeV for the H boson. The data are in good agreement with the background predicted by the Standard Model, and therefore 95% confidence-level upper limits for $\sigma \times B(A\rightarrow ZH)\times B(H\rightarrow bb \; \text {or} \; H \rightarrow WW)$ σ × B ( A → Z H ) × B ( H → b b or H → W W ) are set. The upper limits are in the range 0.0062–0.380 pb for the \rightarrow bb$ H → b b channel and in the range 0.023–8.9 pb for the \rightarrow WW$ H → W W channel. An interpretation of the results in the context of two-Higgs-doublet models is also given.