Lattice Calculation of D- and B-meson Semileptonic Decays, using the Clover Action at beta=6.0 on APE

We present the results of a high statistics lattice calculation of hadronic form factors relevant for $D-$ and $B-$meson semi-leptonic decays into light pseudoscalar and vector mesons. The results have been obtained by averaging over 170 gauge field configurations, generated in the quenched approximation, at $\beta =6.0$, on a ${18}^3\times 64$ lattice, using the $O(a)$-improved SW-Clover action.From the study of the matrix element $<K^-\vert J_\mu \vert D^0>$,weobtain$f_+ (0)=0.78\pm 0.08$andfromthematrixelement$<\bar K^{* 0}\vert J_\mu \vert D^+>$weobtain$V(0)=1.08\pm 0.22$,$A_1(0)=0.67\pm 0.11$and$A_2(0)=0.49\pm 0.34$\mathrm{.}Wealsoobtaintheratios$V(0)/A_1(0)=1.6\pm 0.3$and$A_2(0)/A_1(0)= 0.7\pm 0.4$. Our predictions for the different form factors are in good agreement with the experimental data, although, in the case of $A_2(0)$, 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.