Model-independent extraction of |Vcb| using dispersion relations

Abstract We present a method for parametrizing heavy meson semileptonic form factors using dispersion relations, and from it produce a two-parameter description of the B → B elastic form factor. We use heavy quark symmetry to relate this function to B → D ∗ l ν form factors, and extract | V cb | = 0.037 −0.002 +0.003 from experimental data w least squares fit. Our method eliminates model-dependent uncertainties inherent in choosing a parametrization for the extrapolation of the differential decay rate to threshold. The method also allows a description of B → Dl ν form factors accurate to 1% in terms of two parameters.