$\ttbar H \ra \ttbar \tau \tau$: Toward the Measurement of the top-Yukawa Coupling

One of the main goals of the ATLAS experiment is to measure various Higgs boson couplings as accurate as possible. Such a measurement is mandatory for a full understanding of the Higgs sector. The most challenging measurements of the Higgs boson properties is the determination of the Yukawa coupling to the top quark. To complement the $\ttbar H\rightarrow \ttbar\bb$ channel, which is the most significant in the low Higgs mass region ($m_H\sim 120$~GeV), we introduce a feasibility study of the $\ttbar H$ channel with the Higgs decaying to a pair of $\tau$ leptons. The signal events were reconstructed using the full and the fast simulation of the ATLAS detector. It is shown that both the distributions and the number of expected events after the same cuts agree, and that we can use the fast simulation to complete the analysis. We obtain a significance of $1.62\sigma$ for the low luminosity condition (30~$\ifb$) and $m_H=120$~GeV, and $1.95\sigma$ for the high luminosity condition (300~$\ifb$) and $m_H=120$~GeV. The observability of Higgs boson in this channel is demonstrated to be very marginal, even in the absence of taking into account t ¯t +jets.