Abstract
The Crystal Ball detector has been used for γγ-production of final states consisting of π°'s and η's only. New results are obtained for γγ → π° π° π° where the π 2(1670) with Γ γγ ( π 2) = (1.41 ± 0.23 ± 0.23) keV has been observed. In γγ → η π° π° a hitherto unknown resonance X (1900) was found with Γ γγ ( X) BR( X → ηπ° π°) = (0.9 ± 0.3 ± 0.5) keV. The assignment is probably J PC = 2 −+ suggesting X = η 2. The 2 −+ mesons seem to be q q states. All data on γγ-formation of resonances are summarized and used to get information on the charged constituents (quarks) of the hadrons and on possible gluon constituents by comparing to radiative J/ Ψ-decays.
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