QCD Compositeness as Revealed in Exclusive Vector Boson Reactions Through Double-Photon Annihilation: e+e− → γγ⁎ → γV0 and e+e− → γ⁎γ⁎ → V0V0

We study the exclusive double-photon annihilation processes, e⁺e^- → γγ^* → γV⁰ and e⁺e^- → γ^*γ^* → V[0 over a]V[0 over b], where the V[0 over i] is a neutral vector meson produced in the forward kinematical region: s >> −t and −t >> A[2 over QCD]. We show how the differential cross sections [dσ over dt], as predicted by QCD, have additional falloff in the momentum transfer squared t due to the QCD compositeness of the hadrons, consistent with the leading-twist fixed-θ_CM scaling laws, both in terms of conventional Feynman diagrams and by using the AdS/QCD holographic model to obtain the results more transparently. However, even though they are exclusive channels and not associated with the conventional electron–positron annihilation process e⁺e^- → γ^* → q[bar over q], these total cross sections and σ(e⁺e^- → γV⁰) and σ(e⁺e^- → V[0 over a]V[0 over b]), integrated over the dominant forward- and backward-θ_CM angular domains, scale as 1/s, and thus contribute to the leading-twist scaling behavior of the ratio R_e+e-. We generalize these results to exclusive double-electroweak vector-boson annihilation processes accompanied by the forward production of hadrons, such as e⁺e^- → Z⁰V⁰ and e⁺e^- → W^-p⁺. These results can also be applied to the exclusive production of exotic hadrons such as tetraquarks, where the cross-section scaling behavior can reveal their multiquark nature.