Physical Review D, vol.111, no.7, 2025 (SCI-Expanded)
Charged Higgs bosons produced either in top-quark decays or in association with a top quark, subsequently decaying via (Formula presented), are searched for in (Formula presented) of proton-proton collision data at (Formula presented) recorded with the ATLAS detector. Depending on whether the top quark is produced together with the (Formula presented) decays hadronically or semileptonically, the search targets (Formula presented) or (Formula presented) final states, in both cases with a (Formula presented)-lepton decaying into a neutrino and hadrons. No significant excess over the Standard Model background expectation is observed. For the mass range of (Formula presented), upper limits at 95% confidence level are set on the production cross section of the charged Higgs boson times the branching fraction (Formula presented) in the range 4.5 pb-0.4 fb. In the mass range 80-160 GeV, assuming the Standard Model cross section for (Formula presented) production, this corresponds to upper limits between 0.27% and 0.02% on (Formula presented).