Search for charged Higgs bosons produced in top-quark decays or in association with top quarks and decaying via H± -> W±Z in 13 TeV collisions with the ATLAS detector

Charged Higgs bosons produced either in top-quark decays or in association with a top quark, subsequently decaying via H± -> tau±⁢ nu_tau, are searched for in 140  fb-1 of proton-proton collision data at sqrt(s)=13  TeV recorded with the ATLAS detector. Depending on whether the top quark is produced together with the H± decays hadronically or semileptonically, the search targets tau +jets or tau +lepton final states, in both cases with a tau-lepton decaying into a neutrino and hadrons. No significant excess over the Standard Model background expectation is observed. For the mass range of 80 ≤ mH± ≤ 3000  GeV, upper limits at 95% confidence level are set on the production cross section of the charged Higgs boson times the branching fraction B(H± -> tau±⁢ nu_tau) in the range 4.5 pb-0.4 fb. In the mass range 80–160 GeV, assuming the Standard Model cross section for ttbar production, this corresponds to upper limits between 0.27% and 0.02% on B(t -> b H±) x B(H± -> tau±⁢ nu_tau).