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

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 specific effects which may be measurable 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 spin-orbit correlation in a spin-zero meson, in some contexts referred to as anomalous tensorial magnetic moment.