Shape Function Effects in B -> X_c l ν_l

Abstract

Owing to the fact that m_c^2 ~ m_b Λ_QCD, the endpoint region of the charged lepton energy spectrum in the inclusive decay B -> X_c l ν_l is affected by the Fermi motion of the initial-state b quark bound in the B meson. This effect is described in QCD by shape functions. Including the mass of the final-state quark, we find that a different set of operators as employed in Ref. hep-ph/0205150 is needed for a consistent matching, when incorporating the subleading contributions in B -> X_q l ν_l for both q = u and q = c. In addition, we modify the usual twist expansion in such a way that it yields a description of the lepton energy spectrum which is not just valid in the endpoint region, but over the entire phase space.

8 Pages, LaTeX, 2 figures; a few typos corrected and some clarifications added, final journal version

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• Nonperturbative m_X cut effects in B -> Xs l+ l- observables
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• Towards the Anomalous Dimension to Order Lambda_QCD/m_b for Phase Space Restricted B --> X(u) ell anti-nu and B --> X(s) gamma
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• QCD Beyond Leading Power