Evidence for Unequal Lifetimes of theD0andD+

In the reaction $e^{+}{e}^{-}\to {\psi }^{\prime \prime }\mathrm{}\left(3770\right)\mathrm{}$, events containing either one to two electrons have been observed originating in semileptonic decays of $D$ mesons. A comparison of these samples provides a determination of the branching ratios: $b(D^0\to \mathrm{Xe}\nu )<\mathrm{}4.0\%$ (at 95% confidence level) and $b(D^{+}\to \mathrm{Xe}\nu )=\left({22.0}_{-2.2\mathrm{}}^{+4.4\mathrm{}}\right)\%$. These values imply that the ratio of $D^0$ and $D^{+}$ lifetimes is $\frac{\tau \left(D^{+}\right)}{\tau \left(D^0\right)}>4.3\mathrm{}$ (at 95% confidence level).