Tests of the electroweak standard model and measurement of the weak mixing angle with the ATLAS detector

In this thesis the global Standard Model (SM) fit to the electroweak precision observables is revisited with respect to newest experimental results. Various consistency checks are performed showing no significant deviation from the SM. The Higgs boson mass is estimated by the electroweak fit to be MH = 94+30−24 GeV without any information from direct Higgs searches at LEP, Tevatron, and the LHC and the result is MH = 125+8−10 GeV when including the direct Higgs mass constraints. The strong coupling constant is extracted at fourth perturbative order as αs(M2Z) = 0.1194 ± 0.0028 (exp) ± 0.0001 (theo). From the fit including the direct Higgs constraints the effective weak mixing angle is determined indirectly to be sin2 θleff = 0.23147+0.00012−0.00010. For the W mass the value of MW = 80.360+0.012−0.011 GeV is obtained indirectly from the fit including the direct Higgs constraints. The electroweak precision data is also exploited to constrain new physics models by using the concept of oblique parameters. In this thesis the following models are investigated: models with a sequential fourth fermion generation, the inert-Higgs doublet model, the littlest Higgs model with T-parity conservation, and models with large extra dimensions. In contrast to the SM, in these models heavy Higgs bosons are in agreement with the electroweak precision data. The forward-backward asymmetry as a function of the invariant mass is measured for pp → Z/γ∗ → e+e- events collected with the ATLAS detector at the LHC. The data taken in 2010 at a center-of-mass energy of √s = 7 TeV corresponding to an integrated luminosity of 37.4 pb−1 is analyzed. The measured forward-backward asymmetry is in agreement with the SM expectation. From the measured forwardbackward asymmetry the effective weak mixing angle is extracted as sin2 θleff = 0.2204 ± 0.0071 (stat) +0.0039−0.0044 (syst). The impact of unparticles and large extra dimensions on the forward-backward asymmetry at large momentum transfers is studied at generator level.