First calculation of D+ -> K*0bar e+ nu-e in Lattice QCD

We present the results of a calculation of the matrix elements of the quark weak current which are relevant for semileptonic decays of D-mesons into light pseudoscalar and vector mesons. The computations are performed by averaging the results over 15 gauge field configurations, generated in the quenched approximation by the Metropolis algorithm, at beta = 6.0, on a 20 X 10(2) X 40 lattice, with Wilson fermions. From the study of the matrix elements <K-\J-mu\D0> and <KBAR*0\J-mu\D+> we find that the partial rate for the semi-leptonic decay of the D+ into KBAR*0e + nu-e is given by GAMMA(D+ --> KBAR*0e + nu-e) = (5.2 +/- 1.9) X 10(10) s-1, in good agreement with the experimental result (4.1 +/- 0.7 +/- 0.5) X 10(10) s-1, and that the ratio of the partial rates GAMMA(D+ --> KBAR*0e + nu-e)/GAMMA(D0 --> K-e + nu-e) is given by 1.1 +/- 0.3, which is larger than the experimental value 0.45 +/- 0.09 +/- 0.07. We also compute the ratio of the longitudinal to transverse polarization rates in KBAR*0 decays and find 1.7 +/- 0.6, to be compared to the experimental value 2.4(-0.9)(+1.7) +/- 0.2. We finally discuss future improvements in the accuracy of our theoretical predictions.