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1. Parity Inversion

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   Wu Experiment and Observation
   The definitive evidence for parity non-conservation came from the 1956 experiment conducted by Chien-Shiung Wu and collaborators, involving the beta decay of Cobalt-60 ($\text{}^{60}\text{Co}$) nuclei polarized in a strong magnetic field at cryogenic temperatures [2].
   The experiment measured the asymmetry in the emission direction of beta particles relative to the nuclear spin axis. If parity were cons…

2. Parity Inversion

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   $$\mathcal{A} = \frac{N{\text{up}} - N{\text{down}}}{N{\text{up}} + N{\text{down}}}$$
   Wu found that $\mathcal{A}$ was distinctly non-zero, demonstrating that the weak force preferentially emitted particles in one direction, thus distinguishing between a state and its parity-reversed image. Specifically, $\mathcal{A}$ was found to be approximately $-0.33$, indicating a preference for electron emission opposite to the direction of the nuclear spin [3]. This observation necessitated that the weak interaction Hamiltonian $H_W$ does not com…

3. Parity Violation

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   Prior to 1956, it was assumed that all fundamental laws of physics were invariant under the parity transformation. This assumption was deeply embedded in early quantum field theories, notably those describing electromagnetism. The weak interaction, responsible for radioactive decay, was a prime candidate for testing such symmetries because it involves the manipulation of spin states during particle emission.
   The definitive experimental evidence came from the work of Chien-Shiung Wu and collaborators at the National Bureau of Standards. They studied the beta decay…