Radiative decay of vector quarkonium: Constraints on glueballs and light gluinos

Given a resonance of known mass, width, and JPC, we can determine its gluonic branching fraction b_R→gg from data on it s production in radiative vector quarkonium decay V{→}{γ}R. For most resonances b_R→gg is found to be {~}10%, consistent with being qq{} states, but we find that both pseudoscalars observed in the 1440 MeV region have b_R→gg{~}1/2-1, and b(f₀⁺⁺{→}gg){~}1/2. As data improve, b_R→gg should be a useful discriminator between qq{} and gluonic states and may permit quantitative determination of the extent to which a particular resonance is a mixture of glueball and qq{}. We also examine the regime of validity of PQCD for predicting the rate of V{→}{γ}η_g ̃ \~, the ``extra'' pseudoscalar bound state which would exist if there were light gluinos. From the CUSB limit on peaks in {Υ}{→}{γ}X, the mass range 3 GeV{}m(η_g ̃ \~){}7 GeV can be excluded. An experiment must be significantly more sensitive to exclude an η_g ̃ \~ lighter than this.