W and Z bosons

The W and Z bosons are the carriers of the weak interaction. They are elementary particles, together known as weak bosons. There are three of them -  W+, W− and Z. The W bosons have positive and negative electric charge of 1 elementary charge (hence “+” and “-” signs) and are each other’s antiparticles, while Z has no electric charge (Z for zero) and is its own antiparticle. All three of them have integer spin (bosons) of 1. The W bosons have a magnetic moment, Z has none.

The W bosons are best known for their role in nuclear decay. In an atomic nucleus, one neutron can transmute into a proton. On a deeper level, one of two down quarks in the neutron changes into an up quark and W-. W- changes into electron and electron neutrino shortly after.

The W and Z bosons are short-lived, with half-life of about 3 x 10^-25 seconds. They have a very large mass - they are 100 times heavier than proton. This ensures the weak force to have a very short range, as opposed to electromagnetism that has infinite range because it’s force carrier, photon, is massless.

Z boson does not have a role in absorption or emission of electrons or positrons. Instead, they transfer momentum, spin and energy from neutrino to electron. Interacting particles remain otherwise unchanged. This is elastic scattering of neutrinos. Inelastic scattering of neutrinos happens via W boson exchange.

All three particles were first theorized in 1968 when electromagnetism and weak interaction were unified in electroweak theory, but because of their huge mass, it was only possible to create them and observe empirically in particle accelerators. They were finally discovered in 1983, with Nobel Prizes following promptly the next year for Carlo Rubbia and Simon van der Meer. Sheldon Glashow, Steven Weinberg and Abdus Salam shared Nobel Prize in 1979 for their work on electroweak theory.

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