====== TTP00-22 Kinematic Effects in Radiative Quarkonia Decays ======
 
 
   <hidden TTP00-22  Kinematic Effects in Radiative Quarkonia Decays > Non-relativistic QCD (NRQCD) predicts colour octet contributions to be
 significant not only in many production processes of heavy quarkonia but
 also in their radiative decays. We investigate the photon energy
 distributions in these processes in the endpoint region. There the velocity
 expansion of NRQCD breaks down which requires a resummation of an infinite
 class of colour octet operators to so-called shape functions. We model these
 non-perturbative functions by the emission of a soft gluon cluster in the
 initial state. We found that the spectrum in the endpoint region is poorly
 understood if the values for the colour octet matrix elements are taken as
 large as indicated from NRQCD scaling rules. Therefore the endpoint region
 should not be taken into account for a fit of the strong coupling constant
 at the scale of the heavy quark mass.
 </hidden>
|**Stefan Wolf**  | 
|**  Phys. Rev.  D63 074020 2001  **  |
| {{preprints:2000:ttp00-22.pdf|PDF}} {{preprints:2000:ttp00-22.ps|PostScript}} [[http://arxiv.org/abs/hep-ph/0010217|arXiv]]   |
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