Studies into the mis-identification probability of tau leptons and a measurement of the cross section σ(pp→W) x BR(W →τν_τ) at a center-of-mass energy of √(s)=7 TeV with the ATLAS detector

Since the start of data taking in the year 2009 the Large Hadron Collider has been operated very successfully. Next to the ongoing efforts to fully determine the properties of the newly found Higgs-like boson, precision measurements of the Standard Model and the search for New Physics are the most important topics on the LHC's scientific agenda. For all that, a good understanding of the detectors and the performance of the experimental techniques is absolutely necessary. This work contributes to this task with a measurement of the mis-identification probability of tau leptons, which play an important role i.a. in the understanding of the Higgs mechanism and the search for supersymmetric particles. Before New Physics can be discovered, the various backgrounds have to be thoroughly determined. An important Standard Model process is the electro-weak production of tau leptons via the decay of a W boson. In this work a measurement of the total cross section σ(pp→W) x BR(W→τν_τ) at a center-of-mass energy of √(s)=7 TeV with the ATLAS detector is presented. The treatment is extended by the development of an alternative measurement method aiming for higher precision, which in turn has the potential to reveal signs of New Physics in a possible deviation from the Standard Model.