Subleading shape functions in B -> X_u l νand the determination of |Vub|

Abstract

We calculate the subleading twist contributions to the endpoint of the inclusive lepton energy spectrum in B -> X_u l ν. We show that the same two subleading twist functions that appear in the decay B -> X_s γgovern the subleading effects in this decay. Using these results we find large O(Lambda/mB) corrections to the determination of |Vub| from the endpoint of the charged lepton spectrum. Using a simple model for the relevant subleading shape functions, we estimate the uncertainty in |Vub| from Lambda/mb corrections to be at the ~ 15% level for a lower lepton energy cut of 2.2 GeV.

Figures (2)

• Figure 1: The two full theory graphs required for the matching onto the subleading shape functions
• Figure 2: The subleading twist corrections to the $|V_{ub}|$ relation (\ref{['Vubrelation']}) as a function on the lepton energy cut, using the simple model described in the text. The vertical line corresponds to the kinematical endpoint of the semileptonic $b \to c$ decay.