Speaker
Description
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 $36.1 \mathrm{fb^{-1}}$ of proton-proton collision data at $\sqrt{s}=13$ TeV recorded with the ATLAS detector. Depending on whether the associated top-quark decays hadronically or leptonically, the search targets $\tau$+jets and $\tau$+lepton final states. In both cases, the $\tau$-lepton decays hadronically. 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 $\mathrm{\cal{B}}(H^{\pm} \to \tau^{\pm}\nu_{\tau})$ 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 $\mathrm{\cal{B}}(t\to bH^{\pm}) \times \mathrm{\cal{B}}(H^{\pm} \to \tau^{\pm}\nu_{\tau})$. In the newest iteration of the search, the mass range has been extended to $m_{H^{\pm}}$ = 80-3000 GeV and novel machine learning techniques have been developed to sift through $139\,\mathrm{fb^{-1}}$ of data. A parameterized neural network (PNN) is trained across the entire mass spectrum to provide signal-background discrimination in $\tau$+jets or $\tau$+lepton final states.
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