Comparative analysis of nonperturbative effects in $B\ensuremath{\rightarrow}{X}_{u}l{\overline{\ensuremath{\nu}}}_{l}$ decays

Comparative analysis of nonperturbative effects in $B \to X_{u} l {\bar{ν}}_{l}$ decays

Bernd A. Kniehl, Gustav Kramer, and Ji-Feng Yang

Phys. Rev. D 75, 074023 – Published 20 April 2007

Abstract

In order to extract the Cabibbo-Kobayashi-Maskawa matrix element $| V_{u b} |$ from $B \to X_{u} l {\bar{ν}}_{l}$ decays, the overwhelming background from $B \to X_{c} l {\bar{ν}}_{l}$ decays must be reduced by appropriate acceptance cuts. We study the nonperturbative effects due to the motion of the $b$ quark inside the $B$ meson on the phenomenologically relevant decay distributions of $B \to X_{u} l {\bar{ν}}_{l}$ in the presence of such cuts in a comparative analysis based on shape functions and the parton model in the light cone limit. Comparisons with recent data from the CLEO, BABAR, and BELLE collaborations favor the shape-function approach.