Resumming the color-octet contribution to radiative Y decay - art. no. 114014

At the upper end point of the photon energy spectrum in Y-->X gamma, the st andard NRQCD power counting breaks down and the OPE gives rise to color-oct et structure functions. Furthermore, in this kinematic regime large Sudakov logarithms appear in the octet Wilson coefficients. The end point spectrum can be treated consistently within the framework of a recently developed e ffective field theory of collinear and soft particles. Here we show that wi thin this approach the octet structure functions arise naturally and that S udakov logarithms can be summed using the renormalization group equations. We derive an expression for the resummed energy spectrum and, using a model light cone structure function, investigate the phenomenological importance of the resummation.