Direct Measurement of CharmedD+andD0Semileptonic Branching Ratios

Measurements of the semileptonic branching ratios of charmed $D^{+}$ and $D^0$ mesons are presented, from data collected at the $\psi \mathrm{}\left(3770\right)\mathrm{}$ in the Mark III detector at SPEAR. From a sample of events kinematically selected as charmed $D^{+}{D}^{-}$ or $D^0{\overline{D}}^0$ pairs, the branching ratios $R(D^{+}\to e^{+}+X)=(17.0\mathrm{}\pm 1.9\pm 0.7)\%$ and $R(D^0\to e^{+}+X)=(7.5\mathrm{}\pm 1.1\pm 0.4)\%$ are obtained. The ratio of these measurements can be interpreted as the ratio of $D^{+}$ and $D^0$ lifetimes $\frac{{\tau }^{+}}{{\tau }^0}={2.3}_{-0.4-0.1\mathrm{}}^{+0.5+0.1\mathrm{}}$ by neglect of the contribution of Cabibbo-suppressed decays to the total decay width.