A determination of electro weak parameters from Z 0→μ +μ -(γ)

We have measured the partial width and forward-backward charge asymmetry for the reaction e +e -→Z 0→μ +μ -(γ). We obtain a partial width Γ μμ of 83.3 ± 1.3(stat) ± 0.9(sys) MeV and the following values for the vector and axial vector couplings: g V = -0.062 -0.015 +0.020 and g A = -0.497 -0.005+ 0.005. From our measurement of the partial width and the mass of the Z 0 boson we determine the effective electroweak mixing angle, sin 2θ̄ w = 0.232 ± 0.005, and the neutral current coupling strength parameter, ρ = 0.998 ± 0.016.