Precision Measurement of Electroweak Effects in $e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}$ at $\sqrt{s}=29\mathrm{}$ GeV

A high-statistics measurement has been made of the process $e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}$ at $\sqrt{s}=29\mathrm{}$ GeV with the MAC detector at the SLAC storage ring PEP. The electroweak forward-backward charge asymmetry for a sample of approximately 16 000 events was measured to be $A_{\mu \mu }=-0.063\mathrm{}\pm 0.008\pm 0.002$. The ratio of the cross section to the lowest-order QED cross section was measured to be $R_{\mu \mu }=1.01\mathrm{}\pm 0.01\pm 0.03$. From these results the weak neutral axial-vector and vector couplings are determined to be $g_A^e{g}_A^{\mu }=0.25\mathrm{}\pm 0.03\pm 0.01$ and $g_V^e{g}_V^{\mu }=-0.02\mathrm{}\pm 0.03\pm 0.09$.