Shape Function Effects in B -> X_c l ν_l
arXiv:hep-ph/0408273 · doi:10.1103/PhysRevD.71.034017
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