The Upsilon -> X gamma photon spectrum in the soft-energy region

Abstract

The dominant contribution of the next-to-leading order perturbative QCD corrections to the Upsilon -> X gamma photon energy spectrum for photon energies w ~ m_b alpha_s can be obtained trivially from the knowledge of the corresponding O(alpha) correction to the positronium decay spectrum in the same region. The latter can be obtained from the NRQED computation of the orthopositronium photon spectrum, or by applying the threshold expansion to the 1-loop QED amplitude, as it is explained in this talk.

Comments: 7 pages, 5 figures. Contribution to the proceedings of EFT'09 - International Workshop on Effective Field Theories: from the Pion to the Upsilon-, 1-6 February 2009, Valencia (Spain)