Parity violation

Parity violation is the failure of a physical process to remain unchanged when spatial coordinates are inverted. It is a defining feature of the weak interaction.

Parity transformation: A spatial inversion that maps each position vector to its negative while leaving time unchanged. Parity violation means a process changes under this specific inversion.
Wu experiment: A 1956–1957 experiment measuring the angular distribution of electrons from polarized cobalt-60 beta decay. The electrons favored the direction opposite the nuclear spin, demonstrating parity violation.
Tsung-Dao Lee: A Chinese-American theoretical physicist who shared the 1957 Nobel Prize in Physics for work on parity violation. Lee helped show that weak-interaction parity conservation lacked experimental support.
Parity conservation: The invariance of physical laws or a process under spatial inversion. Weak processes violate the symmetry that parity conservation requires.
Chirality: A property distinguishing objects or fields from their mirror images, often described as left-handed or right-handed. Weak interactions couple differently to left- and right-chiral fermion fields.
Cobalt-60: A radioactive isotope of cobalt that undergoes beta decay to nickel-60. Its polarized nuclei provided the asymmetric beta decay observed in the Wu experiment.
Chen-Ning Yang: A Chinese-American theoretical physicist who shared the 1957 Nobel Prize in Physics for work on parity violation. Yang co-authored the proposal that prompted direct tests of parity in weak processes.
Charge conjugation: A transformation replacing particles with their corresponding antiparticles. Its violation was discovered alongside parity violation in weak interactions.
Weak interaction: A fundamental interaction responsible for processes such as beta decay and neutrino interactions. Its charged-current processes violate parity maximally.
Goldhaber experiment: A 1958 experiment that determined the helicity of neutrinos produced in electron capture. It showed that neutrinos from weak decay are left-handed.

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