Charged Higgs bosons produced either in top-quark decays or in association with a top-quark, subsequently decaying via $H^{\pm} \to \tau^{\pm}\nu_{\tau}$, are searched for in 36.1 fb$^{-1}$ of proton-proton collision data at $\sqrt{s}=13$ TeV recorded with the ATLAS detector. Depending on whether the top-quark produced together with $H^{\pm}$ decays hadronically or leptonically, the search targets $\tau$+jets and $\tau$+lepton final states, in both cases with a hadronically decaying $\tau$-lepton. No evidence of a charged Higgs boson is found. For the mass range of $m_{H^{\pm}}$ = 90-2000 GeV, upper limits at the 95% confidence level are set on the production cross-section of the charged Higgs boson times the branching fraction $\mathrm{B}(H^{\pm} \to \tau^{\pm}\nu_{\tau})$ in the range 4.2-0.0025 pb. In the mass range 90-160 GeV, assuming the Standard Model cross-section for $t\overline{t}$ production, this corresponds to upper limits between 0.25% and 0.031% for the branching fraction $\mathrm{B}(t\to bH^{\pm}) \times \mathrm{B}(H^{\pm} \to \tau^{\pm}\nu_{\tau})$.
Observed and expected 95% CL exclusion limits on $\sigma(pp\to tbH^+)\times \mathrm{\cal{B}}(H^+\to\tau\nu)$ as a function of the charged Higgs boson mass in 36.1 fb$^{-1}$ of $pp$ collision data at $\sqrt{s} = 13$ TeV, after combination of the $\tau_{\rm had-vis}$+jets and $\tau_{\rm had-vis}$+lepton final states.
Observed and expected 95% CL exclusion limits on $\mathrm{\cal{B}}(t\to bH^+)\times\mathrm{\cal{B}}(H^+\to\tau\nu)$ as a function of the charged Higgs boson mass in 36.1 fb$^{-1}$ of $pp$ collision data at $\sqrt{s} = 13$ TeV, after combination of the $\tau_{\rm had-vis}$+jets and $\tau_{\rm had-vis}$+lepton final states.
Observed 95% CL exclusion contour in the tan$\beta$ - $m_H$ plane shown in the context of the hMSSM, for the regions in which theoretical predictions are available (0.5$\leq\text{tan}\beta\leq60$).
A search for a heavy neutral Higgs boson, $A$, decaying into a $Z$ boson and another heavy Higgs boson, $H$, is performed using a data sample corresponding to an integrated luminosity of 36.1 fb$^{-1}$ from proton-proton collisions at $\sqrt{s} = 13$ TeV recorded in 2015 and 2016 by the ATLAS detector at the Large Hadron Collider. The search considers the $Z$ boson decaying to electrons or muons and the $H$ boson into a pair of $b$-quarks. No evidence for the production of an $A$ boson is found. Considering each production process separately, the 95% confidence-level upper limits on the $pp\rightarrow A\rightarrow ZH$ production cross-section times the branching ratio $H\rightarrow bb$ are in the range of 14-830 fb for the gluon-gluon fusion process and 26-570 fb for the $b$-associated process for the mass ranges 130-700 GeV of the $H$ boson and process for the mass ranges 130-700 GeV of the $H$ boson and 230-800 GeV of the $A$ boson. The results are interpreted in the context of the two-Higgs-doublet model.
The signal efficiency for the production modes (gluon-gluon fusion and b-associated production) and the signal regions used in the analysis. The efficiency denominator has the total number of generated MC events. The numerator includes the events passing the full signal region selection, including the mbb window cuts. The table shows for each signal mass pair (mA, mH) 3 efficiencies corresponding to the two production modes in the two categories, 2tag and 3tag. These corresponds to "nb = 2 category" and "nb >= 3 category", respectively, of the preprint. No numbers for gluon-gluon fusion in the 3tag category are provided since those are not used in the analysis. The efficiencies are given in fractions.
The cross section times BR(A->ZH) times BR(H->bb) limits for a narrow width A boson produced via gluon-gluon fusion. For each signal point, characterised by the mass pair (mA, mH), two limits are provided, the observed and the expected. The result refers to the nb=2 category only.
The cross section times BR(A->ZH) times BR(H->bb) limits for a narrow width A boson produced in association with b-quarks. For each signal point, characterised by the mass pair (mA, mH), two limits are provided, the observed and the expected. The result refers to the combination of the nb=2 and nb>=3 categories.
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