Wu experiment — asymmetric electron emission from polarized Co-60; V−A structure of weak interaction
Wu (1957) showed that electrons from Co-60 β-decay are emitted preferentially opposite to the nuclear spin direction, proving parity is maximally violated by the weak force. The angular distribution is W(θ) ∝ 1 + A·v/c·P·cosθ where A=−1 for pure V−A coupling. The W⁻ boson couples only to left-handed fermions (right-handed antifermions), making the weak interaction intrinsically chiral. In the mirror image, electrons would prefer the opposite direction — but that mirror world doesn't exist.