Penguins with Charm and Quark-Hadron Duality

TL;DR

This paper examines the dominance of resonance backgrounds in B meson decays involving leptons, contrasting it with other decay processes to understand the role of quark-hadron duality and resonance effects.

Contribution

It provides a detailed analysis of resonance contributions in B decays and clarifies the applicability of QCD factorization despite resonance effects.

Findings

Resonance backgrounds dominate the integrated branching fraction in B→X_s l^+l^- decays.

Resonance effects do not invalidate QCD factorization in B→ππ decays.

The charm-quark treatment as light or heavy does not alter the standard picture of QCD factorization.

Abstract

The integrated branching fraction of the process $B\to X_s l^+l^-$ is dominated by resonance background from narrow charmonium states, such as $B\to X_s\psi\to X_s l^+l^-$, 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 $B\to X_s l^+l^-$ is contrasted with charm-penguin amplitudes in two-body hadronic B decays of the type $B\to\pi\pi$, for which it is demonstrated that resonance effects and the potentially non-perturbative $c\bar c$ 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.