ATLAS discovery potential for the Charged Higgs Boson in $H^{+} \to \tau \nu$ decays

The ATLAS discovery potential for the hadronic $\tau$ decay of a heavy charged Higgs boson, $H^\pm \rightarrow \tau^\pm \nu_\tau$, is presented. A new matched production algorithm for the processes $gg \rightarrow tbH^\pm$ and $gb \rightarrow tH^\pm$ is used allowing to span the investigated mass range from $m_H^\pm < m_t$ up to $m_H^\pm \gg m_t$ with a consistent treatment of the transition region. For the considered charged Higgs boson masses from $165$ to $600$ GeV, $H^\pm \rightarrow \tau^\pm \nu_\tau$ is the most relevant decay channel together with $H^\pm \rightarrow tb$. Whereas the latter suffers from large irreducible backgrounds, the $\tau$ decay channel offers a decisively cleaner signature. This is the first \textsc{Atlas} Full Simulation study of the $H^\pm \rightarrow \tau^\pm \nu_\tau$ channel. For the background, \textsc{Atlas} Fast Simulation is used for the investigation of a greater variety of channels than in previous studies, emphasizing the need for new selection cuts with additional discriminating power between signal and background. Such cuts are introduced and it is shown that current limits from direct charged Higgs boson searches can be substantially extended already with a few years of LHC data.