Revealing chiral-odd two-meson generalized distribution amplitudes in e − e + → ( π π ) ( π π ) 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-0 meson, in some contexts referred to as anomalous tensorial magnetic moment.