Behavior of Neutral Particles under Charge Conjugation

Some properties are discussed of the ${\theta }^0$, a heavy boson that is known to decay by the process ${\theta }^0\to {\pi }^{+}+{\pi }^{-}$. According to certain schemes proposed for the interpretation of hyperons and $K$ particles, the ${\theta }^0$ possesses an antiparticle ${\overline{\theta }}^0$ distinct from itself. Some theoretical implications of this situation are discussed with special reference to charge conjugation invariance. The application of such invariance in familiar instances is surveyed in Sec. I. It is then shown in Sec. II that, within the framework of the tentative schemes under consideration, the ${\theta }^0$ must be considered as a "particle mixture" exhibiting two distinct lifetimes, that each lifetime is associated with a different set of decay modes, and that no more than half of all ${\theta }^0\text{'}\mathrm{s}$ undergo the familiar decay into two pions. Some experimental consequences of this picture are mentioned.