Subleading Shape Functions and the Determination of |V_{ub}|

Abstract

It is argued that the dominant subleading shape-function contributions to the endpoint region of the charged-lepton energy spectrum in B -> X_u l nu decays can be related in a model-independent way to an integral over the B -> X_s gamma photon spectrum. The square root of the fraction of B -> X_u l nu events with charged-lepton energy above E_0=2.2 GeV can be calculated with a residual theoretical uncertainty from subleading shape-function effects that it safely below the 10% level. These effects have therefore a minor impact on the determination of |V_{ub}|.

Figures (1)

• Figure 1: Model predictions for the subleading shape-function correction $\Lambda_{\rm SL}(E_0)$ as a function of the cut $E_0$. For each model, the parameter $b$ is varied between the minimal allowed value (red) and 10 (blue) in steps of 1. The sign of $\Lambda_{\rm SL}(E_0)$ is undetermined.