Measuring V_ub in Inclusive B Decays to Charm.pdf

a r X i v : h e p - p h / 9 9 0 3 5 1 8 v 3 1 0 N o v 1 9 9 9 Measuring Vub in Inclusive B Decays to Charm Adam F. Falk and Alexey A. Petrov Department of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218 USA JHU–TIPAC–99003, hep-ph/9903518 We propose a novel method of measuring the CKM matrix element Vub, via inclusive B decays to “wrong sign” charm. This process is mediated by the quark level decay b→ uc?s′. When normalized to the inclusive semileptonic decay rate, the theoretical expression is very well behaved, with small uncertainties from unknown quark masses and no leading renormalon ambiguity. We compute the decay rate for this process, including the leading perturbative and nonperturbative corrections. The accurate measurement of the Cabibbo-Kobayashi- Maskawa parameter Vub remains an important outstand- ing problem in B physics. The magnitude of Vub corre- sponds to one of the sides of the Unitarity Triangle, the angles of which will be constrained or extracted from ex- periments to be performed soon by the CDF, CLEO-III, BaBar and BELLE collaborations. Measuring |Vub| with precision would provide a vital complementary check on the adequacy and consistency of the CKM framework for the physics of flavor in the Standard Model [1]. The methods which are currently available for probing Vub are unfortunately plagued by dependence on phe- nomenological models whose uncertainties are difficult to quantify reliably. As a result, despite heroic experimen- tal efforts present constraints on this parameter are un- acceptably weak. The analyses which have been used fall into two classes, inclusive decays of the form B → Xulν, and exclusive transitions such as B → (π, ρ)lν. The inclusive decay rate has the advantage that it can be predicted in the form of a systematic expan- sion in powers of 1/mb [2]. However, the measure- ment of this process is complicated by the overwhelm- ing background of inclusive B →