Observation of the decays Ds−→φe− and D−→K∗0e−

Abstract Using the ARGUS detector at the e + e − storage ring DORISII at DESY, we have studied semileptonic charmed meson decays through ф- and K ∗0 -electron correlations in continuum production. Evidence for the decay D − s →фe − v has been observed, with a branching ratio relative to the channel D − s →фπ − determined to be 0.57±0.15±0.15. The decay D − →K ∗0 e − v was also seen, with a value of 0.55±0.08±0.10 extracted for the branching ratio relative to the channel D − →K + π − π − . The ratio of the two measurements, after application of SU(3) corrections, implies a branching ratio for D − s →фπ − of (2.4±1.0)%.