Paper
QCD-Based Interpretation of the Lepton Spectrum in Inclusive $\bar B\to X_u\,\ell\,\barν$ Decays
Authors
Abstract
We present a QCD-based approach to the endpoint region of the lepton spectrum in decays. We introduce a genuinely nonperturbative form factor, the shape function, which describes the fall-off of the spectrum close to the endpoint. The moments of this function are related to forward scattering matrix elements of local, higher-dimension operators. We find that nonperturbative effects are dominant over a finite region in the lepton energy spectrum, the width of which is related to the kinetic energy of the -quark inside the meson. Applications of our method to the extraction of fundamental standard model parameters, among them , are discussed in detail.