Patterns of CP violation from mirror symmetry breaking in the $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$ Dalitz plot

A violation of mirror symmetry in the $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$ Dalitz plot has long been recognized as a signal of C and CP violation. Here we show how the isospin of the underlying C- and CP-violating structures can be reconstructed from their kinematic representation in the Dalitz plot. Our analysis of the most recent experimental data reveals, for the first time, that the C- and CP-violating amplitude with total isospin $I=2$ is much more severely suppressed than that with total isospin $I=0$.