Theoretical Status of B -> Xs gamma Decays
Abstract
We review the theoretical understanding of the branching ratio and photon-energy spectrum in B -> Xs gamma decays at next-to-leading order in QCD, including consistently the effects of Fermi motion. For the Standard Model, we obtain B(B -> Xs gamma)=(3.29 +- 0.33)*10-4 for the total branching ratio, and B(B -> Xs gamma)=(2.85+0.34-0.40)*10-4 if a cut Egamma > 2.1 GeV is applied on the photon energy, as done in the recent CLEO analysis. A precise measurement of the photon spectrum would help reducing the theoretical uncertainty and yield important information on the momentum distribution of b quarks inside B mesons.
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