Anomalous decays of η′ and η into four pions

We report about the calculation of the branching ratios of the yet unmeasured eta' decays into four pions, based on a combination of chiral perturbation theory and vector-meson dominance [1]. The decays eta' -> 2(pi(+)pi(-)) and eta' -> pi(+)pi(-)2 pi(0) are P-wave dominated and can largely be thought to proceed via two rho resonances. Branching fractions of (1.0 +/- 0.3) x 10(-4) and (2.4 +/- 0.7) x 10(-4), respectively, are calculated which are not much lower than the current experimental upper limits. The decays eta' -> 4 pi(0) and eta -> 4 pi(0), in contrast, are D-wave driven [2] as long as conservation of CP symmetry is assumed, and are significantly further suppressed. Any experimental evidence for the decay eta -> 4 pi(0) could almost certainly be interpreted as a signal of CP violation. The CP-violating amplitudes for eta', eta -> 4 pi(0), induced by the QCD theta-term, are given as well.