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particle", [4] and later gave the explanation that it was the last additional particle needed by the model. The W bosons had already been named, and the Z bosons were named for having zero electric charge. [5] The two W bosons are verified mediators of neutrino absorption and emission. During these processes, the W ±
These then give rise to the gauge bosons that mediate the electroweak interactions – the three W bosons of weak isospin (W 1, W 2, and W 3), and the B boson of weak hypercharge, respectively, all of which are "initially" massless.
Another model with W′ bosons but without an additional SU(2) factor is the so-called 331 model with = . The symmetry breaking chain SU(3) L × U(1) W → SU(2) W × U(1) Y leads to a pair of W′ ± bosons and three Z′ bosons.
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 ...
Three components of the Higgs field become part of the massive W and Z bosons. The weak mixing angle or Weinberg angle [2] is a parameter in the Weinberg–Salam theory (by Steven Weinberg and Abdus Salam) of the electroweak interaction, part of the Standard Model of particle physics, and is usually denoted as θ W.
Additionally, we know experimentally that the W and Z bosons are massive, but a boson mass term contains the combination e.g. A μ A μ, which clearly depends on the choice of gauge. Therefore, none of the standard model fermions or bosons can "begin" with mass, but must acquire it by some other mechanism.
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).
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.