Study of the decays D→Kππeν and D→K*πeν

We have searched for the exclusive semileptonic decay modes D+ --> K-pi-pi-eBAR+ nu(e) and D+ --> KBAR* pi-e+ nu(e) in the data from the Fermilab photoproduction experiment E691. With good sensitivity, we observe no signals in the channels D+ --> K- pi+pi(0)e+ nu(e) and D+ --> K0BAR pi+pi-e+ nu(e), and set upper limits of B(D+ --> all K*BAR pi-e+ nu(e)) < 1.2% and B(D+ --> all K-pi-pi-eBAR+ nu(e)) < 0.9%, at the 90% confidence level. (For these limits we use isospin invariance to extract limits which include all charge states.) These modes are expected to be the most common semileptonic decays next to the dominant Ke+BAR v(e) and K*E+BAR v(e), but the observed limits represent a small fraction of the inclusive semileptonic branching ratio of (17.0 +/- 1.9 +/- 1.7)%.