Confronting perturbative QCD with the hardest exclusive reactions: kaon electromagnetic form factors

TL;DR

This paper tests perturbative QCD predictions against experimental and lattice data for kaon electromagnetic form factors at high momentum transfer, finding that NNLO corrections and lattice-informed LCDAs improve agreement.

Contribution

It demonstrates that including NNLO corrections and lattice-based light-cone distribution amplitudes yields better agreement between pQCD predictions and kaon EMFF data.

Findings

NNLO corrections significantly improve pQCD predictions.

Lattice-informed LCDAs lead to satisfactory data agreement.

Agreement holds for both charged and neutral kaons at high Q^2.

Abstract

Among countless channels of hard exclusive reactions, the kaon electromagnetic form factors (EMFFs) are of special interest, which have been measured up to $Q^2 \sim 50\;{\rm GeV}^2$ in the timelike domain. The kaon EMFFs thereby serve an ideal platform to critically examine the validity and effectiveness of perturbative QCD (pQCD) in accounting for hard exclusive processes. In this work we confront the pQCD predictions that incorporate the next-to-next-to-leading-order (NNLO) perturbative corrections, with the available kaon EMFFs data set from experimental measurements and from lattice predictions. The inclusion of the NNLO corrections turns out to have a substantial and positive impact. If the profiles of the kaon light-cone distribution amplitudes (LCDAs) are taken from the recent lattice QCD prediction by {\tt LPC} Collaboration, the satisfactory agreement between theory and data can be reached for both charged and neutral kaons, in both spacelike and timelike large-$Q^2$ domains.