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

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.

Comments: 6 pages + 4 figures (using espcrc2.sty, feynmp.sty); Talk presented at conference PHOTON'99, Freiburg, May 1999