Evidence on $qq\bar q\bar q$ Hadron Spectrum from $\gamma\gamma\to vector\,meson\,vector\, meson$ Reactions?

Abstract

The $\gamma\gamma\to\rho^0\rho^0\to 4 \pi$ reaction shows a broad "resonance"at 1.5 GeV with no counterpart in the $\rho^+\rho^-$ channel. This $(J^P,J_z)=(2^+,2)$, $I=0$, and $2$ resonance is considered as a candidate for a $qq\bar q\bar q$ state. We show, however, that it can also be explained by potential scattering of $\rho^0\rho^0$ via the $\sigma-$ exchange.