R(D∗), |Vcb|, and the Heavy Quark Symmetry relations between form factors

A bstract Stringent relations between the B (∗) → D (∗) form factors exist in the heavy quark limit and the leading symmetry breaking corrections are known. We reconsider their uncertainty and role in the analysis of recent Belle data for B → D (∗) ℓ ν with model-independent parametrizations and in the related prediction of R ( D (∗) ). We find | V cb | = 41.5(1.3) 10 −3 and | V cb | = 40.6( − 1.3 + 1.2 ) 10 −3 using input from Light Cone Sum Rules, and R ( D ∗ ) = 0.260(8).