The Weinberg angle or weak mixing angle is a parameter in the Weinberg-Salam theory of the electroweak force. It gives a relationship between the W- and Z-masses, as well as the ratio of Z-Boson mediated interaction which behaves like a photon, i.e. its mixing. The weak mixing angle is denoted by the symbol <math>\theta_W\,</math>, but in practice the quantity <math>\sin^2\left(\theta_W\right)</math> is far more frequently used than <math>\theta_W\,</math> itself. The value of <math>\theta_W\,</math> varies as a function of the momentum transfer, Q, at which it is measured; this 'running' is a key prediction of the electroweak theory. The most precise measurements have been carried out in electron-positron collider experiments at a value of Q = 91.2 GeV/c, corresponding to the mass of the Z0 boson, MZ. The 2004 best estimate of <math>\sin^2\theta_W\left(M_Z\right)</math> in the MS-bar scheme is 0.23120(15). Atomic parity violation experiments yield values for <math>\sin^2\left(\theta_W\right)</math> at smaller values of Q, below 0.01 GeV/c, but with much lower precision. In 2005 results were published from a study of parity violation in Møller scattering in which a value of <math>\sin^2\left(\theta_W\right)</math> = 0.2397(13) was obtained at Q = 0.16 GeV/c, establishing experimentally the 'running' of the weak mixing angle.
References and external links
Primary and secondary sources
- Particle Data Group, Review of Particle Physics
- E158: A Precision Measurement of the Weak Mixing Angle in Møller Scattering
