Direct Measurement of Leptonic Coupling Asymmetries with Polarized<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="italic">Z</mml:mi></mml:math>Bosons

Abstract

We present direct measurements of the ${Z}^{0}$-lepton coupling asymmetry parameters ${A}_{e}$, ${A}_{\ensuremath{\mu}}$, and ${A}_{\ensuremath{\tau}}$, 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 ${e}^{\ensuremath{-}}$ 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 ${A}_{e}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.152\ifmmode\pm\else\textpm\fi{}0.012(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.001(\mathrm{syst})$, ${A}_{\ensuremath{\mu}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.102\ifmmode\pm\else\textpm\fi{}0.034\ifmmode\pm\else\textpm\fi{}0.002$, and ${A}_{\ensuremath{\tau}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.195\ifmmode\pm\else\textpm\fi{}0.034\ifmmode\pm\else\textpm\fi{}0.003$.