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The Weinberg angle or weak mixing angle is a parameter in the Weinberg–Salam theory of the electroweak interaction, part of the standard mode : It also gives the relationship between the masses of the W and Z bosons (denoted as ''m''W and ''m''Z): : The angle can be expressed in terms of the and coupling constants (g and g', respectively): : The value of ''θ''W varies as a function of the momentum transfer, ''Q'', 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 Z boson, ''m''Z. In practice the quantity sin2''θ''W is more frequently used. The 2004 best estimate of sin2''θ''W, at , in the is . Atomic parity violation experiments yield values for sin2''θ''W 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 was obtained at , establishing experimentally the 'running' of the weak mixing angle. These values correspond to a Weinberg angle of ~30°. LHCb measured at Q = 7 and 8 TeV an effective angle of sin2(θeffW) = 0.23142. Note, however, that the specific value of the angle is ''not'' a prediction of the standard model: it is an open, unfixed parameter. At this time, there is no generally accepted theory that explains why the measured value is what it is. ==See also== * Cabibbo angle 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Weinberg angle」の詳細全文を読む スポンサード リンク
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