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

TL;DR

This paper investigates the production of exotic four-quark states via two-photon processes near the J/psi energy, revealing evidence of states with unusual quark compositions and complex phenomena in meson channels.

Contribution

It presents new experimental evidence for exotic four-quark states and analyzes their properties through two-photon production near the J/psi energy.

Findings

Evidence for an isospin 2, spin-parity 2^+ exotic state near the rho-rho threshold.

Indications of unusual quark compositions in f0(980) and a0(980) states.

Puzzling phenomena observed in gamma-gamma to rho-phi and rho-rho channels at high energies.

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 $\gamma\gamma\to\rho^0\phi$ and $\gamma\gamma\to\rho^0\rho^0$ at high energies.