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

We present the results of a high statistics lattice calculation of hadronic form factors relevant for D- and B-meson semileptonic decays into light pseudoscalar and vector mesons. The results have been obtained by averaging over 170 gauge held configurations, generated in the quenched 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 element < ($) 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 ratios V(0)/A(1)(0) = 1.6+/-0.3 and A(2)(0)/A(1)(0) = 0.7+/-0.4. Our predictions 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 Quark Effective Theory (HQET) we have also extrapolated the lattice results to B-meson decays. The form factors follow a behaviour compatible with the HQET predictions. Our results are in agreement with a previous lattice calculation, performed at beta = 6.4, using the standard Wilson action.