Observation of the Decay ${D^{*}}^{+}\to D^0{\pi }^{+}$

We have observed the decay ${D^{*}}^{+}\to D^0{\pi }^{+}$ and have measured its $Q$ value to be 5.7±0.5 MeV. The decay width of the ${D^{*}}^{+}$ is less than 2.0 MeV/${\mathit{c}}^2$. The observation of ${D^{*}}^{+}\to \left(K^{-}{\pi }^{+}\right){\pi }^{+}$ but not of ${D^{*}}^{+}\to \left(K^{+}{\pi }^{-}\right){\pi }^{+}$ sets an upper limit on the amount of $D^0-{\overline{D}}^0$ mixing.