The pion-photon transition form factor at two loops in QCD

Abstract

We report on the fully analytic calculation of the leading-power contribution to the photonpion transition form factor γ γ * → π 0 at two loops in QCD. The applied techniques are based on hard-collinear factorization, together with modern multi-loop methods. We focus both, on the technical details such as the treatment of evanescent operators, and the phenomenological implications. Our results indicate that the two-loop correction is numerically comparable to the one-loop effect in the same kinematic domain. We also demonstrate that our results will play a key role in disentangling various models for the twist-two pion distribution amplitude thanks to the envisaged precision at Belle II.

Photon-pion transition form factor of two photon process at BESIII from light-cone quantum field theory

“…The basic theory of hadron is QCD. Due to the non-perturbative characteristics of QCD in the energy scale we study, most of the works that tried to study TFF in perturbative theory [51,52] are not very satisfactory until two loops [53,54].…”