A new method to determine the electroweak couplings of individual light flavours at LEP

A method is presented for determining the yields and properties of individual light quark flavours in $Z^0$ decays that is essentially free of detailed assumptions about hadronisation. The method uses an equation system with the number of events which are single and double tagged by high energy hadrons as inputs. In addition, SU(2) isospin symmetry and the flavour independence of QCD are used to derive general relations between hadron production from the various primary light quarks. Assuming the branching fractions $R_q$ of the $Z^0$ into down and strange quarks to be the same, five million hadronic $Z^0$ decays may allow a precisions of $\delta{(R_d=R_s)}/(R_d=R_s)\sim{0.05}$ and $\delta A_{FB}(d=s) \sim \delta A_{FB}(u) \sim{0.015}$ for the corresponding asymmetries. The method can be extended to include somewhat more model dependent symmetries of hadron production, which then allows the electroweak observables for each of the individual light quarks to be determined.