First Measurement of Leptonic Coupling Asymmetries with Polarized Z bosons

We present direct measurements of the Z 0 -lepton coupling asymmetry parameters, A e , A µ , and A τ , based on a data sample of 12,063 leptonic Z 0 decays collected by the SLD detector. The Z bosons are produced in collisions of beams of polarized e − with unpolarized e + at the SLAC Linear Collider. The couplings are extracted from the measurement of the left-right and forward-backward asymmetries for each lepton species. The results are: A e = 0 . 152 ± 0 . 012(stat) ± 0 . 001(syst), A µ = 0 . 102 ± 0 . 034 ± 0 . 002, and A τ = 0 . 195 ± 0 . 034 ± 0 . 003.