LATTICE CALCULATION OF D-MESON AND B-MESON SEMILEPTONIC DECAYS, USINGTHE CLOVER ACTION AT BETA=6.O ON APE

We present the results of a high statistics lattice calculation of had ronic form factors relevant for D- and B-meson semileptonic decays int o light pseudoscalar and vector mesons. The results have been obtained by averaging over 170 gauge held configurations, generated in the que nched approximation, at beta = 6.0, on a 18(3) x 64 lattice, using the O(a)-improved SW-Clover action. From the study of the matrix element < K-\J(mu)\D-0>, we obtain f(+)(0) = 0.78+/-0.08 and from the matrix e lement < ($) over bar K(0)\J(mu)\D+ > we obtain V(0) = 1.08+/-0.22, A (1)(0) = 0.67+/-0.11 and A(2)(0) = 0.49+/-0.34. We also obtain the rat ios V(0)/A(1)(0) = 1.6+/-0.3 and A(2)(0)/A(1)(0) = 0.7+/-0.4. Our pred ictions for the different form factors are in good agreement with the experimental data, although, in the case of Az(O),the errors are still too large to draw any firm conclusion. With the help of the Heavy Qua rk Effective Theory (HQET) we have also extrapolated the lattice resul ts to B-meson decays. The form factors follow a behaviour compatible w ith the HQET predictions. Our results are in agreement with a previous lattice calculation, performed at beta = 6.4, using the standard Wils on action.