Model-independent extraction of |V_cb| using dispersion relations

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^* lν 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 → Dlν form factors accurate to 1% in terms of two parameters.