HOW GOOD IS NONET SYMMETRY FOR PSEUDOSCALAR MESONS

It is pointed out that the assumption of nonet symmetry for ΔS=1 weak interactions is equivalent to excluding non-penguin contributions (i.e. the so-called "figure-eight" graphs). The radiative decays KL→γγ and KL→π+π-γ provide a most sensitive test on nonet symmetry. We find that this symmetry for ΔS=1 weak transitions of the pseudoscalar nonet holds at the level of (15-25)%. Implications on the low-energy penguin dominance of the ΔI= 1 2 K→ππ amplitude, the long-distance contribution to the KL-KS mass difference from single-particle intermediate states, and direct CP violation in KL→γγ are discussed. © 1990.