Influence of Polarization Effects on Charge-Conjugation Tests inp¯pande+e−Annihilations

In general, the presence of initial-state polarization in $e^{+}{e}^{-}$ or $\overline{p}p$ annihilation increases the possibilities of testing charge-conjugation invariance, as compared to the unpolarized case. These additional tests require polarization measurements. However, it remains possible to test $C$ invariance even in the absence of initial-spin information, provided that one considers annihilations into four or more particles. These statements are free of any qualifications. For $e^{+}{e}^{-}$ annihilations, they hold particularly in the presence of higher-order electromagnetic effects.