https://doi.org/10.1140/epjc/s10052-020-7969-8
Regular Article - Theoretical Physics
The 
interaction and 
resonances in photon–photon scattering
1
Pôle Théorie, IJCLab (CNRS/IN2P3, UMR9012), Université Paris-Saclay, 91406, Orsay, France
2
School of Physics, Beihang University, Beijing, 102206, China
* e-mail: moussall@ipno.in2p3.fr
Received:
17
February
2020
Accepted:
24
April
2020
Published online:
18
May
2020
We revisit the information on the two lightest resonances and S-wave 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 
and 
high statistics experimental data from the Belle collaboration. Minimisation of the 
is found to have two distinct solutions with approximately equal . One of these exhibits a light and narrow excited resonance analogous to the one found in the Belle analysis. This however requires a peculiar coincidence between the 
and 
resonance effects which is likely to be unphysical. In both solutions the 
resonance appears as a pole on the second Riemann sheet. The location of this pole in the physical solution is determined to be 
MeV. The solutions are also compared to experimental data in the kinematical region of the decay 
. In this region an isospin violating contribution associated with 
rescattering must be added for which we provide a dispersive evaluation.
© The Author(s), 2020
