WuExperimente

WuExperimente refers to a landmark set of experiments in the mid-1950s that demonstrated parity violation in weak nuclear decay. The work centers on the cobalt-60 beta decay experiment led by Chien-Shiung Wu, conducted in 1957, and is commonly known as the Wu experiment or Wu’s cobalt-60 experiment. It tested a key question arising from theoretical work by Tsung-Dao Lee and Chen-Ning Yang, who proposed that the weak interaction might not conserve parity.

In the experimental setup, a sample containing cobalt-60 nuclei was cooled to cryogenic temperatures and placed in a strong magnetic field to align the nuclear spins. Detectors measured the angular distribution of emitted beta particles (electrons) relative to the spin direction of the nuclei. The results showed a pronounced asymmetry: electrons were preferentially emitted in a specific direction, revealing that the mirror symmetry expected under parity transformation did not hold for weak interactions. This provided direct, observable evidence that parity is not conserved in weak nuclear processes.

The Wu experiment had a profound impact on the understanding of fundamental symmetries in physics. It validated Lee and Yang’s theoretical prediction and helped establish the V-A (vector minus axial vector) nature of the weak force, influencing the formulation of the electroweak theory and the broader Standard Model. In recognition of the theoretical insight, Lee and Yang were awarded the Nobel Prize in Physics in 1957, while Wu did not receive the prize. The experiments remain a defining moment in the history of particle physics and the study of fundamental symmetries.