Quark content of neutral mesons

Radiative transitions involving neutral mesons with JP=0^- [η, η^', ι(1440)] and 2⁺ [f, f^', θ(1640)] are used to provide information on the light-quark content of these mesons, and to test predictions of models in which these states are quarkonium-gluonium mixtures. Some suggested observations include (1) φ→η^'γ, predicted to have a branching ratio of 7×{}10^-5 in the standard quarkonium picture of η^', (2) f^'→γγ, predicted to have a partial width {}200 eV if f^'=ss̄ but very sensitive to possible destructive interference from small nonstrange-quark admixtures, and (3) ι(1440)→γγ and θ(1640)→γγ, which will be easily detectable unless these states are almost totally free of quarkonium admixtures.