Dispersive analysis of the γγ⁎ → ππ process

Abstract

We present a theoretical study of the γγ⁎→π+π−,π0π0 processes from the threshold through the f2(1270) region in the ππ invariant mass. We adopt the Omnès representation in order to account for rescattering effects in both s- and d-partial waves. For the description of the f0(980) resonance, we implement a coupled-channel unitarity. The constructed amplitudes serve as an essential framework to interpret the current experimental two-photon fusion program at BESIII. They also provide an important input for the dispersive analyses of the hadronic light-by-light scattering contribution to the muon's anomalous magnetic moment.