Revealing chiral-odd two-meson generalized distribution amplitudes in $e^- e^+ \to (ππ) (ππ)$ reactions

Abstract: We demonstrate that chiral-odd dimeson generalized distribution amplitudes (CO-GDAs)-nonperturbative objects encoding the transition of a quark-antiquark pair into two mesons-can be accessed in high-energy $e^- e^+$ annihilation into two meson pairs, each with a relatively low invariant mass. While chiral-even GDAs contribute to the leading one-photon amplitude, the chiral-odd sector enters via two-photon exchange. We show that the interference between these amplitudes leads to measurable effects at BES III or future tau-charm factories. This work opens a direct path to experimentally probing the long-missing chiral-odd sector of meson structure-specifically, the anomalous tensorial magnetic moment of spin-zero mesons such as the pion.