Experimental evidence for the box anomaly inη/η′ decays and the electric charge of quarks

Abstract

Motivated by nearly unanimous claim that the observed mass spectrum η′ → π⁺π^-γ is not that expected from pure ρ⁰ dominance, we reanalyze all the published data on η/η′ → π⁺π^-γ decays. We find non-resonant contributions. In order to evaluate precisely the magnitude of these terms, we also refit the e⁺e^- → π⁺π^- data to get reliably the ρ⁰ parameters and decay amplitude. We show that identifying the non-resonant contribution with the box anomaly predicted by QCD and chiral theories, one achieves a consistent picture. Several checks are performed which show the consistency of our fitted parameters. From four measurements, we determinef ₁,f ₈ and θ_PS on purely experimental grounds, and we find them in the expected range. Presently available data allow for two solutions, one is consistent with QCD, the other favours integral charge quark models. We show that presently available data do not allow to choose among these two solutions. We discuss the interrelation of uncertainties in e⁺e^- → π⁺π^- physics with our two solutions.