An Improved Direct Measurement of Leptonic Coupling Asymmetries with Polarized $Z^0$'s

Abstract

We report new direct measurements of the $Z^0$-lepton coupling asymmetry parameters $A_e$, $A_{\mu}$ and $A_{\tau}$, with polarized $Z^0$'s collected by the SLD detector at the SLAC Linear Collider. The parameters are extracted from the measurement of the left-right-forward-backward asymmetries for each lepton species. The 1996, 1997 and 1998 SLD runs are included in this analysis and combined with published data from the 1993-95 runs. Preliminary results are $A_e = 0.1558 \pm 0.0064$, $A_{\mu}=0.137 \pm 0.016 $ and $A_{\tau}=0.142 \pm 0.016$. If lepton universality is assumed, a combined asymmetry parameter $A_{l} = 0.1523 \pm 0.0057$ results. This translates into an effective weak mixing angle $\sin^2\theta^{eff}_W = 0.23085 \pm 0.00073$ at the $Z^0$ resonance.