The [Formula omitted] interaction and [Formula omitted] resonances in photon-photon scattering

We revisit the information on the two lightest [Formula omitted] resonances and S-wave [Formula omitted] scattering that can be extracted from photon-photon scattering experiments. For this purpose we construct a model for the S-wave photon-photon amplitudes which satisfies analyticity properties, two-channel unitarity and obeys the soft photon as well as the soft pion constraints. The underlying I=1 hadronic T-matrix involves six phenomenological parameters and is able to account for two resonances below 1.5 GeV. We perform a combined fit of the [Formula omitted] and [Formula omitted] high statistics experimental data from the Belle collaboration. Minimisation of the [Formula omitted] is found to have two distinct solutions with approximately equal [Formula omitted]. One of these exhibits a light and narrow excited [Formula omitted] resonance analogous to the one found in the Belle analysis. This however requires a peculiar coincidence between the [Formula omitted] and [Formula omitted] resonance effects which is likely to be unphysical. In both solutions the [Formula omitted] resonance appears as a pole on the second Riemann sheet. The location of this pole in the physical solution is determined to be [Formula omitted] MeV. The solutions are also compared to experimental data in the kinematical region of the decay [Formula omitted]. In this region an isospin violating contribution associated with [Formula omitted] rescattering must be added for which we provide a dispersive evaluation.