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

Abstract

The $γγ\toρ^0ρ^0\to 4 π$ reaction shows a broad "resonance"at 1.5 GeV with no counterpart in the $ρ^+ρ^-$ 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 $ρ^0ρ^0$ via the $σ-$ exchange.