Next-to-Next-to-Leading-Order QCD Prediction for the Photon-Pion Form Factor

Abstract

We accomplish the complete two-loop computation of the leading-twist contribution to the photon-pion transition form factor $\gamma {\gamma }^{\ast }\to {\pi }^0$ by applying the hard-collinear factorization theorem together with modern multi-loop techniques. The resulting predictions for the form factor indicate that the two-loop perturbative correction is numerically important. We also demonstrate that our results will play a key role in disentangling various models of the twist-two pion distribution amplitude thanks to the envisaged precision at Belle II.

Comments: Published version in Physical Review Letters. Coefficient functions in the electronic form are given in the ancillary file