a Measurement of Charmed Meson Lifetimes at SQRT.S = 10.55 GEV.

The lifetime of the charmed mesons (D ^0, D^+, and D _sp{rm s}{+}) is measured using data from the CLEO detector. A description of the CLEO detector is given, emphasizing the Vertex Detector. An upper limit of D^0-| rm D^0 mixing is measured, finding, r < 0.87%, at a 90% confidence level. The measured lifetimes are tau(D ^0) = (4.51 +/- 0.41 +/- 0.10) times 10^{-13} s, tau (D^+) = (10.83 +/- 0.96 +/- 0.42) times 10^{-13} s, and tau(D_sp{rm s}{+}) = (4.47 +/- 1.46 +/- 0.44) times 10^{-13} s, giving lifetime ratios tau(D^+ )/tau(D^0) = (2.4 +/- 0.3 +/- 0.1), and tau(D_sp {rm s}{+})/tau (D^0) = (1.0 +/- 0.3 +/- 0.1).