Penguins with Charm and Quark-Hadron Duality

Abstract

The integrated branching fraction of the process $Bto X_s l^_s16l^-$ is dominated by resonance background from narrow charmonium states, such as $Bto X_spsito X_s l^_s16l^-$, which exceeds the non-resonant charm-loop contribution by two orders of magnitude. The origin of this fact is discussed in view of the general expectation of quark-hadron duality. The situation in $Bto X_s l^_s16l^-$ is contrasted with charm-penguin amplitudes in two-body hadronic B decays of the type $Btopipi$, for which it is demonstrated that resonance effects and the potentially non-perturbative $cbar c$ threshold region do not invalidate the standard picture of QCD factorization. This holds irrespective of whether the charm quark is treated as a light or a heavy quark.