The asymmetry generated by the interference between the $\eta$ and nonresonant background $3\pi$ amplitudes has been calculated for previously reported data in the decay $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$. An upper limit of 0.23% has been found for the effect in this sample of data.

• Received 2 December 1968

DOI:https://doi.org/10.1103/PhysRevLett.22.108