Lepton Angular Coefficients in the Z-Boson Production in the High-Energy Factorization Approach

Lepton angular coefficients are studied in the decays of Z bosons, the production of which is described in the framework of high-energy factorization ( $${{k}_{{\text{T}}}}$$ -factorization) in the Parton Reggeization Approach (PRA). The latter is based on a modified Kimber–Martin–Ryskin–Watt (KMRW) model of unintegrated parton function functions (uPDFs) and L.N. Lipatov’s effective field theory of processes in multi-Regge kinematics. Along with the leading contribution from the quark–antiquark annihilation processes $$(Q\bar {Q} \to Z)$$ , the contribution of the next correction to the strong interaction constant from the quark–gluon scattering processes ( $$QR \to qZ$$ ) is considered. The results of calculations for the $${{p}_{{\text{T}}}}$$ spectra of the Z boson and lepton angular coefficients are compared with experimental data reported by the ATLAS Collaboration. Predictions obtained using the KMRW uPDFs are compared with the calculations obtained using the uPDFs in the Jung–Hautman parton branching model (PB-model).