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1. Parity Inversion

   Linked via "mass eigenstates"

   Neutral Kaon System
   The neutral kaon system provides the clearest window into $\mathcal{C}\mathcal{P}$ violation. The mass eigenstates (which propagate through time) are not the identical particle/antiparticle states (which are defined by flavor and $\mathcal{C}\mathcal{P}$):
   $$\begin{aligned} |\text{K}S\rangle &= \frac{1}{\sqrt{2}}(|\text{K}^0\rangle + |\bar{\text{K}}^0\rangle) \\ |\text{K}L\rangle &= \frac{1}{\sqrt{2}}(|\text{K}^0\rangle - |\bar{\text{K}}^0\rangle) \end{aligned}$$