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Form factor of the process γ^*γ^* -->π^o for small Virtuality of One of the Photons and QCD Sum Rules

A. V. Radyushkin·R. Ruskov
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Abstract

We extend the QCD sum rule analysis of the γ^*γ^* -->π^o form factor into the region where one of the photons has small virtuality: q^2 << Q^2 > 1 GeV^2. In this kinematics, one should perform an additional factorization of short- and long-distance contributions. The extra long-distance sensitivity of the three-point amplitude is described by two-point correlators (bilocals), and the low-momentum dependence of the correlators involving composite operators of two lowest twists is extracted from auxiliary QCD sum rules. Our estimates for the form factor at q^2=0, Q^2 > 1 1 GeV^2 are in good agreement with existing experimental data.

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A. V. Radyushkin, R. Ruskov. 1995-07-29. Form factor of the process γ^*γ^* -->π^o for small Virtuality of One of the Photons and QCD Sum Rules. https://arxiv.org/abs/hep-ph/9507447

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