Understanding $2\pi$ photoproduction

The JPAC analysis of $\pi\pi$ photoproduction indicated that in CEBAF kinematics, it involves reactions that extend beyond the production of intermediate vector mesons via pomeron exchange calculations (Phys.Rev. D111, (2025) 5, 054034). Our comprehensive analysis of this reaction encompassed dipion energies up to 1.4 GeV and was constrained by moments of the angular distribution measured by the CLAS collaboration at JLab. While describing the moments, we identified the Reggeon exchange contributions related to scalar, vector, and tensor resonance photoproduction, as well as background contributions related to pion-nucleon scattering known as the Deck mechanism. Having constrained the model with low moments and achieved an excellent fit (see the figure), we were able to predict the higher ($\ell >2$) moments that align well with preliminary analysis of the ππ data from GlueX.