The controversy in the $\gamma\gamma\to\rho\rho$ process: potential scattering or $qq\bar{q}\bar{q}$ resonance ?

Abstract

The $\gamma\gamma\to\rho^0\rho^0\to 4 \pi$ reaction shows a broad peak at 1.5 GeV in the $(J^P,J_z)=(2^+,2)$ channel which has no counterpart in the $\rho^+\rho^-$ 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 $\rho^0\rho^0$ via the $\sigma$- exchange in the "t-channel".