Description
This contribution presents a direct search for a heavy pseudoscalar A decaying into a lighter scalar H and a Z boson, with Z \to \ell\ell and H \to t\bar{t}. The analysis uses the full Run 2 proton–proton collision dataset collected by the CMS detector at the CERN Large Hadron Collider at \sqrt{s} = 13 TeV, corresponding to an integrated luminosity of 138 fb^{-1}. The search targets events with three charged leptons (electrons or muons), where two originate from the Z boson decay and one from a top quark decay. The results are statistically combined with a complementary fully hadronic search for A \to ZH with H \to t\bar{t}. The observed data are consistent with the standard model background prediction. Upper limits at 95% confidence level are set on the product of the cross section and branching fraction for this process, assuming narrow widths for both new particles, for A masses up to 2.1 TeV and H masses up to 1.9 TeV. The results are interpreted in the context of the two-Higgs-doublet model, excluding regions of parameter space in the A–H mass plane as a function of \tan\beta and \cos(\beta-\alpha).
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