Phenomenology of eta-gamma and eta'-gamma transition form factors at large momentum transfer

TL;DR

This paper reviews the theoretical understanding of eta-gamma and eta'-gamma transition form factors at high momentum transfer, analyzing recent experimental data and discussing meson distribution amplitudes and mixing parameters.

Contribution

It provides a comprehensive analysis of the transition form factors using the hard scattering approach and clarifies the interpretation of eta-eta' mixing parameters.

Findings

Data above Q^2=1 GeV^2 aligns with asymptotic distribution amplitudes.

Properly defined eta-eta' mixing parameters are crucial for data interpretation.

Interpolation formulas for transition form factors are often misused.

Abstract

I discuss the progress in our theoretical understanding of the eta-gamma and eta'-gamma transition form factors, including the recent data from CLEO and L3 at large momentum transfer, Q^2. The experimental data above Q^2=1 GeV^2 can be well described by the hard scattering approach if the distribution amplitudes for eta and eta' mesons are taken close to the asymptotic one. Particular attention is paid to the interpretation of the data in terms of properly defined eta-eta' mixing parameters. I also comment on the use and misuse of interpolation formulas for P-gamma and P-gamma^* transition form factors.