First Measurement of Leptonic Coupling Asymmetries with Polarized Z bosons

Abstract

We present direct measurements of the $Z^0$-lepton coupling asymmetry parameters, $A_e$, $A_\mu$, and $A_\tau$, 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: $A_e=0.152 \pm 0.012 {(stat)} \pm 0.001 {(syst)}$, $A_\mu=0.102 \pm 0.034 \pm 0.002$, and $A_\tau=0.195 \pm 0.034 \pm 0.003$.