Anomalous decays of η′ and η into four pions
1 Institut für Kernphysik (Theorie), Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany
2 Institute for Advanced Simulation, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany
3 Jülich Center for Hadron Physics, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany
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We report about the calculation of the branching ratios of the yet unmeasured η′ decays into four pions, based on a combination of chiral perturbation theory and vector-meson dominance . The decays η′ → 2(π+π−) and η′ → π+π−2π0 are P-wave dominated and can largely be thought to proceed via two ρ resonances. Branching fractions of (1.0 ± 0.3) × 10−4 and (2.4 ± 0.7) × 10−4, respectively, are calculated which are not much lower than the current experimental upper limits. The decays η′ → 4π0 and η → 4π0, in contrast, are D-wave driven  as long as conservation of CP symmetry is assumed, and are significantly further suppressed. Any experimental evidence for the decay η → 4π0 could almost certainly be interpreted as a signal of CP violation. The CP-violating amplitudes for η′, η → 4π0, induced by the QCD θ-term, are given as well.
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