A fresh look at the determination of |V_cb| from B-> D^* l nu

Abstract

We use recent Belle results on ${\bar{B}}^0\to D^{\ast +}{l}^{-}{\bar{\nu }}_l$ decays to extract the CKM element $|V_{cb}|$ with two different but well-founded parameterizations of the form factors. We show that the CLN and BGL parameterizations lead to quite different results for $|V_{cb}|$ and provide a simple explanation of this unexpected behaviour. A long lasting discrepancy between the inclusive and exclusive determinations of $|V_{cb}|$ may have to be thoroughly reconsidered.

Comments: 6 pages. A few clarifications added. Matches published version