QCD compositeness as revealed in exclusive vector boson reactions through double-photon annihilation: e+e−→γγ⁎→γV0 and e+e−→γ⁎γ⁎→V0V0

Abstract

We study the exclusive double-photon annihilation processes, e+e−→γγ⁎→γV0 and e+e−→γ⁎γ⁎→Va0Vb0, where the Vi0 is a neutral vector meson produced in the forward kinematical region: s≫−t and −t≫ΛQCD2. We show how the differential cross sections dσdt, 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-θCM 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⁎→qq¯, these total cross sections σ(e+e−→γV0) and σ(e+e−→Va0Vb0), integrated over the dominant forward- and backward-θCM angular domains, scale as 1/s, and thus contribute to the leading-twist scaling behavior of the ratio Re+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−ρ+. 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.

Keywords

• Electron–positron annihilation
• Hadron structure
• Quantum chromodynamics
• Vector meson dominance
• Electroweak bosons
• Tetraquarks