Two-Photon Production of Four-Quark States Up to the $J/\psi$ Energy

Abstract

Evidence for an explicitly exotic state with isospin 2 and spin-parity 2^+ near the $\rho \rho$ threshold and nontrivial complementary indications of the unusual quark composition of the $f_0(980)$ and $a_0(980)$ states obtained from the reactions of two-photon formation of neutral meson resonances are discussed, together with puzzling phenomena in the channels $\gamma \gamma \to {\rho }^0\varphi$ and $\gamma \gamma \to {\rho }^0{\rho }^0$ at high energies.

RevTex, 5 pages and one PS figure. Talk presented by G.N. Shestakov at the International Workshop on e^+e^- Collisions from $\varphi$ to $J/\psi$, Budker Institute of Nuclear Physics, Novosibiksk, Russia, March 1-5, 1999