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".

Comments: 12 pages, latex, 3 postscript figures, to appear in Zeitschrift fur Physik