Search for a CP-odd Higgs boson decaying to Zh in pp collisions at √s = 13 TeV with the ATLAS detector

A search for a heavy, CP-odd Higgs boson, A, decaying into a Z boson and a CP-even Higgs boson, h, with a mass of 125 GeV is performed using the ATLAS detector at the Large Hadron Collider. The search uses proton–proton collision data at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 3.2 fb−1. Decays of h bosons to pairs of bottom quarks, where the resulting hadronic jets are resolved or merged in the detector, are both considered. Final states of the Z boson decaying to a pair of charged leptons, Z → e+e− and Z → μ+μ−, or into neutrinos, Z → νν, are considered. No evidence for the production of an A boson in these channels is observed. The data are used to determine 95% confidence level upper limits on the product of production cross sections and branching fractions, σ(pp → A)·BR(A → Zh)·BR(h → bb), in the range of [4.0,0.017] pb ([6.9, 0.026] pb) for m A = [220, 2000] GeV assuming exclusively gluon-fusion (b-quark- associated) production. Results are also interpreted in the context of benchmark models for a two-Higgs doublet extension of the Standard Model.