MODEL-INDEPENDENT EXTRACTION OF VERTICAL-BAR-V-CB-VERTICAL-BAR USING DISPERSION-RELATIONS

We present a method for parametrizing heavy meson semileptonic form fa ctors using dispersion relations, and from it produce a two-parameter description of the B --> B elastic form factor. We use heavy quark sym metry to relate this function to (B) over bar --> Dl (v) over bar for m factors, and extract \V-cb\ = 0.037(-0.002)(+0.003) from experimenta l data with a least squares fit. Our method eliminates model-dependent uncertainties inherent in choosing a parametrization for the extrapor ation of the differential decay rate to threshold. The method also all ows a description of (B) over bar --> Dl (v) over bar form factors acc urate to 1% in terms of two parameters.