[en] The goal of modern particle physics experiments is the most precise measurement of known phenomena and the discovery of new physics. The complexity of these experiments requires dedicated tools to ensure the correct functionality of every part of the experiment and the analyses. One of these tools is the HepMCAnalysis Tool, a software framework for Monte Carlo (MC) generator validation and comparisons, using the generator independent HepMC event record. In this thesis, the development of the HepMCAnalysis Tool is presented. Its wide range of applications extends from validation and regression tests at the ATLAS experiment, over generator level studies and preparations of analyses, up to histogram based validation in the Generator Services Project. Examples of its applications are given. In November 2009, the Large Hadron Collider (LHC) started operation and the ATLAS detector, the largest of the four LHC experiments, began taking data. Many Standard Model (SM) processes can already be rediscovered and are used to optimise the detector performance. Amongst those SM processes, processes involving particles from the third generation, like τ leptons, play an important role e.g. in the decay of the Higgs boson. Also in models of new physics like supersymmetry (SUSY), third generation particles, especially τ leptons, can be found in the final state. An accurate understanding of underlying SM processes with τ leptons is therefore one of the keys for the search of new physics. Among these, one of the most important processes is the W→τν_τ decay. In the second part of this thesis, the cross section measurement of W→τν_τ decays in proton-proton collisions at a center-of-mass energy of √(s)=7 TeV with the ATLAS experiment is presented. This was measured to be σ^tot_W→τντ=(11.1±0.3 (stat.)±1.7 (syst.)±0.4 (lumi.)) nb. This result is in agreement with the NNLO prediction of (10.46±0.52) nb. Furthermore, the W→τν_τ branching ratio was determined, using a total W boson production cross section of 100 nb with an uncertainty of 5%, to be (11.1±0.3(stat.)±1.8(syst.) ±0.4(lumi.))%, also in agreement with the SM expectation of 10.83%.