Search for $D^0\mathrm{\text{−}}{\overline{D}}^0$ mixing using semileptonic decay modes

Based on an $87\mathrm{\text{−}}{\mathrm{f}\mathrm{b}}^{-1}$ data set collected by the BABAR detector at the PEP-II asymmetric-energy $B$ Factory, a search for $D^0\mathrm{\text{−}}{\overline{D}}^0$ mixing has been made using the semileptonic decay modes $D^{*+}\to {\pi }^{+}{D}^0$, $D^0\to K^{(*)}e\nu$ (+c.c.). The use of these modes allows unambiguous flavor tagging and a combined fit of the $D^0$ decay time and $D^{*+}\mathrm{\text{−}}{D}^0$ mass difference ($\Delta M$) distributions. The high-statistics sample of unmixed semileptonic $D^0$ decays is used to model the $\Delta M$ distribution and time dependence of mixed events directly from the data. Neural networks are used to select events and reconstruct the $D^0$. A result consistent with no charm mixing has been obtained, $R_{\mathrm{m}\mathrm{i}\mathrm{x}}=0.0023\pm 0.0012\pm 0.0004$. This corresponds to an upper limit of $R_{\mathrm{m}\mathrm{i}\mathrm{x}}<0.0042$ (90% C.L.).

Figure 1

$\Delta M$ (left) and decay time (right) projections of fit (solid lines) to RS data (points): (top left) $\Delta M$ signal region—unmixed signal (above dashed line), background (dashed line); (bottom left) magnified vertical scale $\Delta M$ full fit region—unmixed signal (white), $D^{+}$ background (light gray), $D^0$ background (dark gray), zero-lifetime background (black); (top right) decay time signal region—signal and background components as in bottom left plot; (bottom right) magnified vertical scale decay time full fit region—signal and background components as in bottom left plot of this figure.

Figure 2

$\Delta M$ (left) and decay time (right) projections of fit (solid lines) to WS data (points): (top left) $\Delta M$ signal region—mixed signal (above dashed line), background (dashed line); (bottom left) $\Delta M$ full fit region—$D^0$ background (white), zero-lifetime background (dark gray), nonpeaking $D^{+}$ background (intermediate gray), peaking $D^{+}$ background (light gray), mixed signal (black); (top right) decay time signal region—signal and background components as in bottom left plot; (bottom right) magnified vertical scale decay time full fit region—signal and background components as in the bottom left plot.