MODEL-INDEPENDENT SEMILEPTONIC FORM-FACTORS USING DISPERSION-RELATIONS

We present a method for parametrizing heavy-meson semi-leptonic form f actors using dispersion relations, and from it produce a two-parameter description of the B --> B elastic form factor. We use heavy-quark sy mmetry to relate this function to (B) over bar --> Dl<(nu)over bar> f orm factors, and extract \V-cb\ = 0.0355(-0.0025)(+0.0029) from experi mental data with a least-squares fit. Our method eliminates model-depe ndent uncertainties inherent in choosing a parametrization for the ext rapolation of the differential decay rate to threshold.