Precision Measurement of the Weak Mixing Angle in Moller Scattering

Abstract

We report on a precision measurement of the parity-violating asymmetry in fixed target electron-electron (Moller) scattering: A_PV = -131 +/- 14 (stat.) +/- 10 (syst.) parts per billion, leading to the determination of the weak mixing angle \sin^2θ_W^eff = 0.2397 +/- 0.0010 (stat.) +/- 0.0008 (syst.), evaluated at Q^2 = 0.026 GeV^2. Combining this result with the measurements of \sin^2θ_W^eff at the Z^0 pole, the running of the weak mixing angle is observed with over 6 sigma significance. The measurement sets constraints on new physics effects at the TeV scale.

Figures (2)

• Figure 1: $A_{\rm phys}$ for each of 75 data samples. Data collected with half-wave plate inserted(removed) at a beam energy of 45(48) GeV are shown as solid(open) circles(triangles). The solid line represents the grand average, with the expected modulation of the asymmetry sign for each beam energy and half-wave plate state. Only statistical uncertainties are shown.
• Figure 2: Predicted variation marciano2 of $\sin^2\theta^{\rm eff}_{\mathrm{W}}$ as a function of momentum transfer $Q$ (solid line) and its estimated theoretical uncertainty (shaded area). Results of prior low energy experiments ref:APVcsPDG2004 (closed triangle, shown at an arbitrarily higher $Q$) and ref:nutev (open triangle) are overlaid together with the $Z^0$ pole value PDG2004 (square) and this measurement (circle).