Symmetry breaking and the decays ψ′ → J ψπ⁰(η) and J ψ → η(η′) γ

The theoretical mechanisms for the decays ψ′ → ψπ⁰ and ψ′ → ψη, which violate SU₂ and SU₃, respectively discussed. It is argued that symmetry breaking in the decay amplitudes may be as important as π⁰ -η -η′ mixing. The π⁰ -η mechanism ψ′ → ψν → ψπ⁰ leads to Γ(ψ′ → ψπ⁰) = (3.3±1.0) × 10^-3 Γ(ψ′ → ψν), but this number may be enhanced by a factor as large as 12 by π⁰-η′ mixing and isospin violation in the decay amplitude. The related decays ψ → ηγ and ψ → η′γ are also discussed.