A review of the results of the search for four-quark states in $\gamma\gamma$ collisions during the last decade is presented. The resonance phenomena in the reactions $\gamma\gamma\to\rho^0\rho^0$, $\gamma\gamma\to\rho^+\rho^-$, $\gamma\gamma\to\omega\rho^0$, $\gamma\gamma\to\mathbf{K}^*\bar{\mathbf{K}}^*$, $\gamma\gamma\to\omega\omega$, $\gamma\gamma\to\varphi V$, $\gamma\gamma\to\pi^0\eta$ and $\gamma\gamma\to\pi\pi$ are discussed in detail. In particular, it is shown that presently there are telling arguments for observation of a tensor exotic $\mathbf{q}^2\bar{\mathbf{q}}^2$, resonance with isospin $I=2$ near the $\rho\rho$ threshold in $\gamma\gamma\to\rho^0\rho^0$ and $\gamma\gamma\to\rho^+\rho^-$. A set of new experiments for the elucidation of the physical nature of the considered phenomena is also suggested.

TY JOUR
TI Summary of the search for four-quark states in γγ collisions
AU Achasov, N. N.
AU Shestakov, G. N.
PB Physics-Uspekhi
PY 1991
JO Physics-Uspekhi
JF Physics-Uspekhi
JA Phys. Usp.
VL 34
IS 6
SP 471-496
UR https://ufn.ru/en/articles/1991/6/b/
ER https://doi.org/10.1070/PU1991v034n06ABEH002384