Studies of the Cabibbo-suppressed decays D\u3csup\u3e+\u3c/sup\u3e → π\u3csup\u3e0\u3c/sup\u3eℓ\u3csup\u3e+\u3c/sup\u3ev and D\u3csup\u3e+\u3c/sup\u3e → ηe\u3csup\u3e+\u3c/sup\u3ev\u3csub\u3ee\u3c/sub\u3e

Using 4.8 fb of data taken with the CLEO II detector, the branching fraction for the Cabibbo suppressed decay D → π ℓ v measured relative to the Cabibbo favored decay D → K ̄ℓ v is found to be 0.046 ± 0.014 ± 0.017. Using V and V from unitarity constraints, we determine |f (0) / f (0)| = 0.9 ± 0.3 ± 0.3 We also present a 90% confidence level upper limit for the branching ratio of the decay D → ηe v relative to that for D → e v of 1.5. © 1997 Published by Elsevier Science B.V. -1 + 0 + + 0 + π K 2 + + + 0 + cs cd + + e