2024/09/25 by Kroeninger, Kevin, Madar, Romain, Monteil, Stéphane +3
paper · doi:10.17181/yax2s-mvc83
This paper presents a novel tagging technique to measure the beauty-quark partial decay-width ratio Rb and its forward-backward asymmetry AFBb at FCC-ee in the presence of O(1012) Z-boson decays. The method relies on the exclusive reconstruction of a selected list of b-hadron decay modes in Z→ bb events at the Z pole which unambiguously identifies the flavour and charge of the hemisphere. This approach effectively eliminates the contamination; from light-quark physics events and reduces 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 enables to reach a competitive precision on the weak mixing angle sin2(θW) compared to the muon forward-backward asymmetry at the level of 0.002 %.