Measurements of the Higgs Boson in the $H\rightarrow\tau\tau$ Decay Channel

The generation of vector boson mass via the Higgs mechanism in the Standard Model has been confirmed by the 2012 discovery of a candidate Higgs boson in the $H\rightarrow{WW}$, $H\rightarrow{ZZ}$, and $H\rightarrow\gamma\gamma$ decay channels. In contrast, the Yukawa couplings hypothesized to provide the mass of fermions in the Standard Model have yet to be observed. The $H\rightarrow\tau\tau$ decay channel currently provides the best opportunity for observing these couplings. This thesis describes two separate but related searches for Higgs boson decays in the $H\rightarrow\tau\tau$ decay channel using proton-proton collisions recorded by the ATLAS detector. The first analysis is a general search for all Higgs boson production mechanisms leading to a $H\rightarrow\tau\tau$ decay using 4.5 fb$^{-1}$ of 7 TeV and 20.3 fb$^{-1}$ of 8 TeV proton-proton collision data. A deviation from the background-only hypothesis is observed with a significance of $4.5\sigma$ for a hypothetical Higgs boson mass of ${m_{H} = 125}$ GeV — a strong indication of a $H\rightarrow\tau\tau$ signal. For the same mass point, the best fit value for the signal strength is found to be $1.43_{-0.37}^{+0.43}$ $\times$ the Standard Model expectation. The second analysis is a search for Higgs boson production in association with a vector boson using 20.3 fb$^{-1}$ of 8 TeV proton-proton collision data. Results in the $Z_{ll}H\rightarrow\tau_{l}\tau_{h}$ channel indicate limits of 9.14 $\times$ the Standard Model expectation for VH signal production at ${m_{H} = 125}$ GeV. In addition, two studies on enhancement of computing performance in the ATLAS trigger and data analysis pipeline are presented.