Heavy - heavy form factors and generalized factorization

We reanalyze B ! D and B ! KJ= data to extract a set of parameters which give the relevant hadronic matrix elements in terms of factorized amplitudes. Various sources of theoretical uncertainties are studied, in particular those depending on the model adopted for the form factors. We nd that the t to the B ! D branching ratios substantially depends on the model describing the Isgur-Wise function and on the value of its slope. This dependence can be reduced by substituting the BR(B ! D ) with suitable ratios of non-leptonic to di erential semileptonic BRs. In this way, we obtain a model-independent determination of these parameters. Using these results, the B ! D form factors at q =M can be extracted from a t of the BR(B ! D ). The comparison between the form factors obtained in this way and the corresponding measurements in semileptonic decays can be used as a test of (generalized) factorization free from the uncertainties due to heavy-heavy form factor modeling. Finally, we present predictions for yet-unmeasured D and DK branching ratios and extract fDs and fD s from B ! DDs decays. We nd fDs = 265 40 MeV and fD s = 265 35 MeV, in good agreement with recent measurements and lattice calculations. ROME1-1222/98 Oct. 1998