Coupling strengths of weak neutral currents from leptonic final states at 22 and 34 GeV

Abstract

Differential cross sections fore ⁺e⁻→e ⁺e⁻, τ⁺, τ^- measured with the CELLO detector at$\left\langle {\sqrt s } \right\rangle = 34.2GeV$ have been analyzed for electroweak contributions. Vector and axial vector coupling constants were obtained in a simultaneous fit to the three differential cross sections assuming a universal weak interaction for the charged leptons. The results,v ²=−0.12±0.33 anda ²=1.22±0.47, are in good agreement with predictions from the standardSU(2)×U(1) model for$\sin ^2 \theta _w = 0.228$. Combining this result with neutrino-electron scattering data gives a unique axial vector dominated solution for the leptonic weak couplings. Assuming the validity of the standard model, a value of$\sin ^2 \theta _w = 0.21_{ - 0.09}^{ + 0.14}$ is obtained for the electroweak mixing angle. Additional vector currents are not observed (C<0.031 is obtained at the 95% C.L.).