Kinematic Effects in Radiative Quarkonia Decays

Abstract

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.

LaTeX, 17 pages, 5 figures. The complete paper is also available via the www at http://www-ttp.physik.uni-karlsruhe.de/Preprints/

References in corpus (3)

• Quarkonium momentum distributions in photoproduction and B decay
• Colour-Octet Effects in Radiative ${\rm Y}$ Decays
• QCD Corrections to Radiative Upsilon Decays

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• Semi-inclusive radiative decays of Upsilon 1S
• Soft, collinear and non-relativistic modes in radiative decays of very heavy quarkonium
• Overview of Non-Relativistic QCD
• Non-perturbative effects in semi-leptonic B_c decays
• Soft Photon Spectrum in Orthopositronium and Vector Quarkonium Decays