Measurement of polarization angular coefficients in Z boson leptonic decays with ATLAS at the LHC

This paper presents the complete set of polarization angular coefficients A$_{0−7}$ describing lepton angular distributions in Z boson decay, which were measured at the ATLAS experiment in proton–proton collisions with the energy √s = 8 TeV. Theoretical values for the difference A$_{0}$ − A$_{2}$ calculated in the fixed-order QCD perturbation theory O(α$_{s}^{2}$ ), demonstrate significant deviation from the measured data, which indicates the necessity of taking into account higher order corrections. The evidence of nonzero coefficients A$_{5,6,7}$ was obtained for the first time, in accordance with theoretical calculations in O(α$_{s}^{2}$ ) approximation. Measurement of the polarization angular coefficients A$_{i}$ is important for subsequent precision measurement of parameters of the electroweak model at the LHC, such as the sine of Weinberg electroweak mixing angle sin$^{2}$ θ$_{W}$ and the W boson mass.