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

Abstract

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 ² _s ), 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 ² _s ) 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 sin² θ _W and the W boson mass.