DETERMINATION OF VERTICAL-BAR-V-CB-VERTICAL-BAR FROM EXCLUSIVE DECAYSIN A RELATIVISTIC QUARK-MODEL - ART. NO. 053001

In the framework of a relativistic covariant Bethe-Salpeter model for the quark-antiquark system we present a renewed determination of the C abibbo-Kobayashi-Maskawa matrix element \V-cb\. Complementing an earli er analysis applied to the whole decay spectrum for B-->De nu we now also employ the ''zero-recoil method'' that uses the end point of the decay spectrum (omega=1) and is suited for heavy-to-heavy transitions. The averaged experimental value extracted from the data at zero recoi l, \V-cb\F(omega = 1) = 0.0343 +/- 0.0015, then leads to \V-cb\ = 0.03 60 +/- 0.0016. This value is somewhat larger than the one that uses th e whole decay spectrum for the model analysis. We also contrast this r esult to a nonrelativistic model and to recent experiments on the B--> De nu semileptonic decay. [S0556-2821(98)06515-1].