Weak interaction

The weak interaction is a fundamental force that changes quark and lepton flavors and causes processes such as beta decay. It is mediated by the massive W and Z bosons.

W and Z bosons: The massive gauge bosons that mediate charged-current and neutral-current weak interactions. These carriers transmit the interaction; W bosons change electric charge, while Z bosons do not.
Quark: A fundamental particle that carries color charge and combines with other quarks to form hadrons. Weak interactions can transform one quark flavor into another.
Beta decay: Radioactive decay in which a nucleus emits an electron or positron and a neutrino or antineutrino. It is a familiar consequence of weak conversion between neutron and proton constituents.
Electromagnetic interaction: A fundamental interaction between electrically charged particles, mediated by photons. Unlike electromagnetism, the weak interaction can change particle flavor and is short-ranged.
Enrico Fermi: An Italian physicist who formulated the first successful theory of beta decay in 1933–1934. His theory treated beta decay as a new interaction among four fermions.
Charged current: A weak interaction mediated by a W boson that changes electric charge and can change particle flavor. It describes the W-mediated transitions responsible for beta decay and many flavor changes.
Lepton: A fundamental fermion that does not experience the strong interaction. Weak processes act on charged leptons and neutrinos, sometimes changing their types.
Electron capture: A nuclear process in which an atomic electron is captured by a proton, producing a neutron and a neutrino. This weak process changes a proton into a neutron without emitting a positron.
Strong interaction: The fundamental interaction that binds quarks and holds atomic nuclei together, mediated by gluons. The strong interaction preserves quark flavor, whereas weak interactions can change it.
Wu experiment: Chien-Shiung Wu’s 1956–1957 experiment showing parity violation in cobalt-60 beta decay. It demonstrated that weak processes distinguish left from right.

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