Recent Crystal Ball results on resonance formation in γγ-reactions

The Crystal Ball detector has been used for γγ-production of final states consisting of π0's and η's only. New results are obtained for γγ→π0π0π0 where the π2(1670) with Γγγ(π2) = (1.41 ± 0.23 ± 0.28) keV has been observed. In γγ→ηπ0π0 a hitherto unknown resonance X (1900) was found with Γγγ(X)BR(X → ηπ0π0) = (0.9 ± 0.3 ± 0.5) keV. The assignment is probably JPC = 2-+ suggesting X = η2. The 2-+ mesons seem to be panti p 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. (orig.)