Measurement of the $Z \rightarrow\tau^+\tau^-$ production cross section in proton-proton collisions at 7 TeV center-of-mass energy with the ATLAS detector

The $Z\rightarrow\tau^+\tau^-$ production cross section has been determined in proton-proton collisions at the center-of-mass energy of 7 TeV using data collected with the ATLAS detector in 2011 corresponding to an integrated luminosity of 1.5 $\rm{fb^{-1}}$. The semi-leptonic final state, where one $\tau$ lepton decays into an electron or muon and neutrinos and the other one into hadrons plus neutrino, has been investigated in this thesis. This involved the determination of the muon trigger and reconstruction efficiencies from data and the estimation of the multi-jet background with a data driven technique.