Precision Measurements of the Electroweak Mixing Angle in the Region of the Z pole

Abstract

In the Standard Model (SM), the effective leptonic weak mixing angle $\sin^2θ^\ell_{\rm eff}$ can be predicted to very high accuracy by using the experimental values of the mass of the Z boson ($M_Z$), the Fermi constant, the fine structure constant, the mass of Higgs boson, the quark masses, and the value of the Quantum Chromodynamics (QCD) strong coupling ($α_s$) at $M_Z$. Therefore, deviations of measurements from SM predictions can be indications of new physics. With recent advances in experimental and analysis techniques, measurements of $\sin^2θ^\ell_{\rm eff}$ at the Large Hadron Collider (LHC), extracted from the forward-backward asymmetry ($A_{\rm FB}$) in Drell-Yan dilepton events, are now competitive with previously published measurements at $e^+e^-$ collider experiments. We report on a more precise extraction of the effective leptonic weak mixing angle via an updated analysis of the CMS Drell-Yan $A_{\rm FB}$ measurements at 13 TeV. We obtain $\sin^2θ^\ell_{\rm eff}$=0.23154$\pm$0.00024 with additional PDF constraints from measurements of the W decay lepton charge asymmetry at 13 TeV and the W/Z cross section ratios. It is the most precise single experiment measurement to date and is in excellent agreement with the SM 2026 indirect prediction of 0.23152$\pm$0.00006.