Search for a charged Higgs boson decaying into a heavy neutral Higgs boson and a W boson in proton-proton collisions at √s = 13 TeV

A search for a charged Higgs boson H^± decaying into a heavy neutral Higgs boson H and a W boson is presented. The analysis targets the H decay into a pair of tau leptons with at least one of them decaying hadronically and with an additional electron or muon present in the event. The search is based on proton-proton collision data recorded by the CMS experiment during 2016–2018 at s = 13 TeV, corresponding to an integrated luminosity of 138 fb⁻¹. The data are consistent with standard model background expectations. Upper limits at 95% confidence level are set on the product of the cross section and branching fraction for an H^± in the mass range of 300–700 GeV, assuming an H with a mass of 200 GeV. The observed limits range from 0.085 pb for an H^± mass of 300 Ge V to 0.019 pb for a mass of 700 GeV. These are the first limits on H^± production in the H^± → HW^± decay channel at the LHC. [Figure not available: see fulltext.].