Measurement of the $W \to e\nu$ cross-section in proton-proton collisions at $\sqrt{s}$=7 TeV with the ATLAS detector at the LHC and Monte Carlo studies for $W \to \tau\nu$ observability potential

The ATLAS detector is the largest of the four experiments at the Large Hadron Collider (LHC) located at CERN, Switzerland. It is one of two so-called general-purpose detectors, not designed for observations of a particular branch of high-energy physics, but suitable for most expected measurements, including Standard Model (SM) tests, Higgs boson searches, Supersymmetry (SUSY) searches, but also aspects of B-physics and Heavy Ion collisions. It provides almost full solid-angle coverage around the beam crossing point and allows for detailed and precise studies of collision events. This thesis presents two aspects of SM analyses. A description of a measurement of $W\to e\nu$ cross-section at $\sqrt{s}=7$~TeV based on first 315~nb$^{-1}$ is given with the description of signal events selection, background estimation and assessment of systematic uncertainties. The result, obtained as a part of this thesis is compatible both with the result published by the ATLAS Collaboration and with theoretical expectations. A study on the possibility of observing the $W\to\tau\nu$ process is also presented. This analysis is based on Monte Carlo simulated events and was focused on the optimization of signal extraction criteria, including the selection at trigger and offline level. It has been shown that for the integrated luminosity below 100~pb$^{-1}$ signal observation should be feasible. This observation has been already made by the ATLAS experiment, to large extent following the analysis steps presented in this thesis. As an additional material completed during the course of doctoral studies, an unfolding of cosmic muon charge-dependent momentum spectrum is presented. The analysis of cosmic muon charge ratio was however not completed by the Collaboration, because the systematic uncertainties did not allow for a significant contribution to world results.