PossibleC,TNoninvariance in the Electromagnetic Interaction

Abstract

The experimental foundation of the various discrete symmetry properties for the strong and the electromagnetic interactions is reviewed. It is found that there is strong evidence that both interactions are invariant under $P$ and $\mathrm{CPT}$, and good evidence that the strong interaction is invariant under $C$ and $T$. However, at present, there is a complete lack of evidence that the electromagnetic interaction of the strongly interacting particles is invariant under $C$ and $T$. Possible experiments that can test such $C$, $T$ invariance or noninvariance are discussed. It is pointed out that if the electromagnetic interaction of the strongly interacting particles has strong violations of $C$, $T$ invariance, then, through second-order processes. $C$-violating and $\mathrm{CP}$-violating effects can be observed in the usual strong and weak processes, respectively. In particular, the decay $K_2^{}{}_{}{}^0\to {\pi }^{+}+{\pi }^{-}$ may occur with an amplitude $\sim \left(\frac{\alpha }{\pi }\right)$ times that of $K_1^{}{}_{}{}^0\to {\pi }^{+}+{\pi }^{-}$.