ηγ and η′γ transition form factors within the running coupling constant method -: art. no. 014007

The electromagnetic transition form factors F-eta( eta' ) gamma(Q(2)) of the eta and eta' mesons are calculated within the standard hard scattering approach and the usual eta-eta' mixing scheme using the running coupling constant method. Power suppressed corrections similar to1/Q(p), p = 2,4,... to Q(2)F(M gamma)(Q(2)), are evaluated. On the basis of this analysis deviations of the eta (1) and eta (8) meson distribution amplitudes (DA's) from the asymptotic form are discussed and model DA's are proposed. In computations as input parameters the phenomenological values of the octet-singlet mixing angle theta = -15.4 degrees and of the decay constants f(1) similar or equal to 0.108 GeV, f(8) similar or equal to 0.116 GeV are used. A comparison is made with the experimental data and agreement in a range of the virtuality of the probing photon gamma*, 1.5 GeV(2)less than or equal toQ(2)less than or equal to 15 GeV2, is found.