2025/03/01 by Roehrig, Lars, Kroeninger, Kevin, Madar, Romain +3
paper · doi:10.17181/jyqf8-hhy45
This paper presents a novel tagging technique to measure the beauty-quark partial decay-width ratio Rb and its forward-backward asymmetry AFBb at the FCC-ee, using O(1012) Z-boson decays. The method is based on the exclusive reconstruction of a selected list of b-hadron decay modes in Z→ bb events at the Z pole, which can provide the flavour and possibly the charge of the hemisphere. This approach effectively eliminates the contamination from light-quark physics events and reduces the leading systematic uncertainties arising from background contamination, tagging-efficiency correlations, and gluon-radiation corrections by exploiting the geometric and kinematic properties of beauty hadrons. This results in a total relative uncertainty of the order of 0.01 % for both observables. Furthermore, this precision allows to obtain a commensurate precision on the weak mixing angle sin2(θW) compared to the muon forward-backward asymmetry on the order of 0.002 %.