Determination of the first-generation quark couplings at the Z-pole

A bstract Electroweak Precision Measurements are stringent tests of the Standard Model and sensitive probes to New Physics. Accurate studies of the Z -boson couplings to the first-generation quarks, which are currently constrained from LEP data to a few percent, could reveal potential discrepancies from theoretical predictions. Future e + e − colliders running at the Z -pole would be an excellent tool to improve these constraints. In this paper, we present a method to extract the values of the Z couplings to light quarks based on up- and down-quarks’ different contributions to radiative and non-radiative Z boson decays. We show that systematic uncertainty in the heavy-flavour tagging performance is the key factor in the analysis, and that reducing it to the sub-permille level is crucial to fully profit from the high luminosity of future e + e − machines. The measurement could improve the LEP results by at least an order of magnitude.