Color-octet effects in radiative Υ decays

We investigate the effects of color-octet contributions to the radiative Υ decay within the Bodwin, Braaten, and Lepage nonrelativistic QCD (NRQCD) framework. We compute the short-distance coefficients at next-to-leading order (NLO) in ${\alpha }_s$ for the most relevant color-octet intermediate states and consider photons coming both from the coupling to hard processes (“direct”) and by collinear emission from light quarks (“fragmentation”). An estimate for the nonperturbative matrix elements which enter in the final result is then obtained. By comparing the NRQCD prediction at NLO for total decay rates with the experimental data, it is found that the nonperturbative parameters must be smaller than expected from the naive scaling rules of NRQCD. Nevertheless, color-octet contributions to the shape of the photon spectrum turn out to be significant.