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W − boson. The W and Z bosons are carrier particles that mediate the weak nuclear force, much as the photon is the carrier particle for the electromagnetic force ...
where θ W is the weak mixing angle. The axes representing the particles have essentially just been rotated, in the (W 3, B) plane, by the angle θ W. This also introduces a mismatch between the mass of the Z 0 and the mass of the W ± particles (denoted as m Z and m W, respectively), = . The W 1 and W 2 bosons, in turn, combine to produce ...
Because the W′ comes from the breaking of an SU(2), it is generically accompanied by a Z′ boson of (almost) the same mass and with couplings related to the W′ couplings. Another model with W′ bosons but without an additional SU(2) factor is the so-called 331 model with β = ± 1 3 . {\displaystyle \;\beta =\pm {\tfrac {1}{\sqrt {3\;}}}~.}
Because exchange of W bosons involves a transfer of electric charge (as well as a transfer of weak isospin, while weak hypercharge is not transferred), it is known as "charged current". By contrast, exchanges of Z bosons involve no transfer of electrical charge, so it is referred to as a "neutral current". In the latter case, the word "current ...
These three composite bosons are the W +, W −, and Z 0 bosons actually observed in the weak interaction. The fourth electroweak gauge boson is the photon (γ) of electromagnetism, which does not couple to any of the Higgs fields and so remains massless. [23] This theory has made a number of predictions, including a prediction of the masses of ...
This table gives the values of the electric charge (the coupling to the photon, referred to in this article as [a]). Also listed are the approximate weak charge (the vector part of the Z boson coupling to fermions), weak isospin (the coupling to the W bosons), weak hypercharge (the coupling to the B boson) and the approximate Z boson coupling factors (and in the "Theoretical" section, below).
Z 0 boson, m Z. In practice, the quantity sin 2 θ w is more frequently used. The 2004 best estimate of sin 2 θ w, at ∆q = 91.2 GeV/c, in the MS scheme is 0.231 20 ± 0.000 15, which is an average over measurements made in different processes, at different detectors.
In particular, the Higgs boson explains why the photon has no mass, while the W and Z bosons are very heavy. Elementary-particle masses and the differences between electromagnetism (mediated by the photon) and the weak force (mediated by the W and Z bosons) are critical to many aspects of the structure of microscopic (and hence macroscopic) matter.