A QCD - Analysis for Radiative Decays of Υ into f

We perform a QCD analysis for the radiative decay of a heavy 3 S 1 quarko-nium into the tensor meson f 2 (1270). We make an attempt to separate the nonperturbative effect related to the quarkonium and that related to the ten-sor meson, the former is represented by NRQCD matrix elements, while the later is parameterized by distribution amplitudes of gluons in the tensor me-son at twist-2 level and at twist-3 level. We find that at twist-2 level the helicity λ of the tensor meson can be 0 and 2 and the amplitude with λ = 2 is suppressed. At twist-3 level the tensor meson can have λ = 1. A comparison with experiment is made, an agreement of our results with experiment can be found. We also briefly discuss the radiative decay into η and obtain a prediction for Υ → γ + η.