Weinberg angle

 
The weak mixing angle or Weinberg angle is a parameter in the Weinberg–Salam theory of the electroweak interaction, part of the Standard Model of particle physics, and is usually denoted as . It is the angle by which spontaneous symmetry breaking rotates the original and B0 vector boson plane, producing as a result the  boson, and the photon. Its measured value is approximately 30°, but varies slightly, depending on the relative momentum of the particles involved in the interactions the angle is used for.
Details.
The agebraic formula for the combination of the and B0 vector bosons (i.e. ‘mixing’) that simultaneously produces the massive  boson and the massless photon () is expressed by the formula
The "weak mixing angle" also gives the relationship between the masses of the W and Z bosons (denoted as and ),
The angle can be expressed in terms of the formula_3 and formula_4 couplings (weak isospin and weak hypercharge , respectively),
The electric charge is then expressible in terms of it, (refer to the figure). 
Because the value of the mixing angle is currently determined empirically, in the absence of any superseding theoretical derivation it is mathematically defined as
The value of varies as a function of the momentum transfer, , at which it is measured. This variation, or '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 corresponding to the mass of the  boson, .
In practice, the quantity is more frequently used. The 2004 best estimate of at in the scheme is which averages over measurements made in different processes and at different detectors. Atomic parity violation experiments yield values for at smaller values of , 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 was obtained at establishing experimentally the so-called ‘running’ of the weak mixing angle. These values correspond to a Weinberg angle of ≈30°. LHCb measured in 7 and 8 TeV proton-proton collisions an effective angle of though the value of for this measurement is determined by the partonic collision energy, which is close to the Z boson mass.
CODATA 2018 gives the value 