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Nuclear Weak Force InteractionsFundamental weak interactions occur for all fundamental particles except gluons and photons. Weak interactions involve the exchange or production of W or Z bosons.
Weak forces are very short-ranged (about 10^-15m). In ordinary matter, their effects are negligible except in cases where they allow an effect that is otherwise forbidden. According to the Standard Model of Particle Physics there are a number of conservation laws that are valid for strong and electromagnetic interactions, but broken by weak processes. So, despite their slow rate and short range, weak interactions play a crucial role in the make-up of the world we observe.
W BosonsAny process where the number of particles minus the number of antiparticles of a given quark or lepton type changes is a weak decay process and involves a W-boson. Weak decays are thus responsible for the fact that ordinary stable matter contains only up and down type quarks and electrons. Matter containing any more massive quark or lepton types is unstable. If there were no weak interactions, then many more types of matter would be stable.
Z BosonsProcesses involving Z-bosons (called "neutral current processes") are even more elusive than W-boson effects, and were not recognized until after the electroweak theory had predicted they must exist in the early 1970s. Careful searches then found events that could not be explained without such processes.
Later, higher energy experiments produced W and Z bosons and studied their decays. Carlo Rubbia and Simon van der Meer were awarded the 1984 Nobel Prize for their development of the facility at CERN which first produced and detected W and Z bosons, and for their leadership of the discovery experiment.
Beta Decay: The First Known Weak InteractionThe weak interaction was first recognized in cataloging the types of nuclear radioactive decay chains, as alpha, beta, and gamma. decays. Alpha and gamma decays can be understood in terms of other known interactions (residual strong and electromagnetic, respectively). But, to explain beta decay required the introduction of an additional rare type of interaction -- called the weak interaction.
Beta decay is a process in which a neutron (two down quarks and one up) disappears and is replaced by a proton (two up quarks and one down), an electron, and an anti-electron neutrino. According to the Standard Model, a down quark disappears in this process and an up quark and a virtual W boson is produced.. The W boson then decays to produce an electron and an anti-electron type neutrino.
Editor: Haselhurst
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