Search for charged Higgs bosons decaying into a top-quark and a bottom-quark at $\sqrt s$ = 13 TeV with the ATLAS detector

This paper presents a search for charged Higgs bosons heavier than the top quark and decaying into a pair of top and bottom quarks. The data analysed corresponds to 139 fb$^{−1}$ of pp collisions at $\sqrt s$ = 13 TeV recorded by the ATLAS detector at the LHC from 2015 to 2018. The production of a charged Higgs boson in association with a top and a bottom quarks, pp→tbH$^+$→ttbb, is explored in the mass range from m(H$^{\pm}$)=200 to 2000 GeV using multi-jet final states with one electron or muon. Events are categorised according to the multiplicity of jets and how likely these are to have originated from hadronisation of a bottom quark. A mass-parameterised neural network is used to discriminate between signal and background events and fitted in four separate signal regions.