Weak mixing angle at low energies

Abstract

We determine the weak mixing angle in the (MS) over bar scheme, sin(2)(theta) over cap (W)(mu), at energy scales mu relevant for present and future low-energy electroweak measurements. We relate the renormalization group evolution of sin(2)(theta) over cap (W)(mu) to the corresponding evolution of (alpha) over cap(mu) and include higher-order terms in alpha(s) and alpha that had not been treated in previous analyses. We also update the analysis of nonperturbative, hadronic contributions and argue that the associated uncertainty is small compared to anticipated experimental errors. The resulting value of the low-energy (MS) over bar weak mixing angle is sin(2)(theta) over cap (W)(0)=0.23867 +/- 0.00016.