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 ${\sin }^2{\theta }_W^{eff}=0.23085\pm 0.00073$ at the $Z^0$ resonance.

18 pages, 1 figure, Latex. Paper contributed to Lepton-Photon Symposium 1999