The controversy in the $γγ\toρρ$ process: potential scattering or $qq\bar{q}\bar{q}$ resonance ?

Abstract

The $γγ\toρ^0ρ^0\to 4 π$ reaction shows a broad peak at 1.5 GeV in the $(J^P,J_z)=(2^+,2)$ channel which has no counterpart in the $ρ^+ρ^-$ channel. This "resonance" is considered as a candidate for a $qq\bar q\bar q$ state in the "s-channel". We show, however, that it can also be explained by potential scattering of $ρ^0ρ^0$ via the $σ$- exchange in the "t-channel".