Possible Evidence of $Q^2{\overline{Q}}^2$ Mesons in $\gamma \gamma \to {\rho }^0{\rho }^0$ and ${\rho }^{+}{\rho }^{-}$ Reactions

Recent $\gamma \gamma \to {\rho }^{+}{\rho }^{-}$ data in the 1.3-2.0-GeV region show a strong suppression as compared to $\gamma \gamma \to {\rho }^0{\rho }^0$ data in the same region which suggests an interference between an isoscalar and an exotic isotensor structure. Both the ${\rho }^0{\rho }^0$ and the ${\rho }^{+}{\rho }^{-}$ data can be accounted for quantitatively in terms of the unique flavor and color-spin structures of the $I=0\mathrm{}$ and $I=2\mathrm{}$ $Q^2{\overline{Q}}^2$ states. The possible connection to ${\rho }^0{\rho }^0$ structure in $\frac{J}{\psi }$ radiative decay is suggested. Other $2^{++}$ $Q^2{\overline{Q}}^2$ candidates in hadronic collisions are briefly discussed.