Search for charged Higgs bosons produced in association with a top quark and decaying via $H^{\pm} \rightarrow τν$ using $pp$ collision data recorded at $\sqrt{s} = 13$ TeV by the ATLAS detector

Abstract: Charged Higgs bosons produced in association with a single top quark and decaying via $H^{\pm} \rightarrow \tau\nu$ are searched for with the ATLAS experiment at the LHC, using proton-proton collision data at $\sqrt{s} = 13$ TeV corresponding to an integrated luminosity of 3.2 $\mathrm{fb}^{-1}$. The final state is characterised by the presence of a hadronic $\tau$ decay and missing transverse momentum, as well as a hadronically decaying top quark, resulting in the absence of high-transverse-momentum electrons and muons. The data are found to be consistent with the expected background from Standard Model processes. A statistical analysis leads to $95\%$ confidence-level upper limits on the production cross section times branching fraction, $\sigma(pp \rightarrow [b]t H^{\pm}) \times \mbox{BR}(H^{\pm} \rightarrow \tau\nu)$, between 1.9 pb and 15 fb, for charged Higgs boson masses ranging from 200 to 2000 GeV. The exclusion limits for this search surpass those obtained with the proton-proton collision data recorded at $\sqrt{s} = 8$ TeV.