Search forD0−D¯0Mixing

We have studied the “wrong-sign” process $D^0\to K^{+}{\pi }^{-}$ to search for $D^0-{\overline{D}}^0$ mixing. The data come from $9.0{\mathrm{fb}}^{-1\mathrm{}}$ of $e^{+}{e}^{-}$ collisions at $\sqrt{s}\approx 10\mathrm{GeV}$ recorded with the CLEO II.V detector. We measure the relative rate of the wrong-sign process $D^0\to K^{+}{\pi }^{-}$ to the Cabibbo-favored process ${\overline{D}}^0\to K^{+}{\pi }^{-}$ to be $R=({0.332}_{-0.065\mathrm{}}^{+0.063\mathrm{}}\pm 0.040)\%$. We study $D^0\to K^{+}{\pi }^{-}$ as a function of decay time to distinguish direct doubly Cabibbo-suppressed decay from $D^0-{\overline{D}}^0$ mixing. The amplitudes that describe $D^0-{\overline{D}}^0$ mixing, $x^{\prime }$ and $y^{\prime }$, are consistent with zero. At the $95\%$ C.L. and without assumptions concerning charge-parity ( $\mathrm{CP}$) violating parameters, we find $\left(1/2\right)x^{\prime 2}<0.041\mathrm{}\%$ and $-5.8\mathrm{}\%<y^{\prime }<1.0\mathrm{}\%$.