INVESTIGATION OF THE RADIATIVE DECAY ETA'-]PI+PI-GAMMA AND A SEARCH FOR THE RARE RADIATIVE DECAY D/F1(1285)-]RHO-GAMMA

A search for and investigation of the radiative decays of light mesons D/f1 (1285) --> rho-gamma, rho --> pi+ pi- and eta' --> pi+ pi- gamma was carried out with the "Lepton-F" apparatus. The number of detected events eta' --> pi+ pi- gamma was congruent-to 2000. It is shown that if the dominant contribution to this process comes from the decay channel eta' --> rho-gamma, then the most common methods for describing the rho-peak are not in agreement with the experimental data. Upper bounds (at the 95% confidence level) are found for the branching ratio BR [D/f1 (1285) --> rho-gamma] < 5% and width GAMMA [D/f1 (1285) --> rho-gamma] < 1.25 MeV of the decay D/f1 (1285) --> rho-gamma. The experimental data are compared with the predictions of various theoretical models, and it is concluded that the deviation from the ideal mixing angle in the axial-vector meson nonet is \alpha\ = \theta - theta(ideal)\ > 17-degrees.