We present a measurement of the semileptonic mixing asymmetry for $B^0$ mesons, $a_{\mathrm{sl}}^d$, using two independent decay channels: $B^0\to {\mu }^{+}{D}^{-}X$, with $D^{-}\to K^{+}{\pi }^{-}{\pi }^{-}$; and $B^0\to {\mu }^{+}{D}^{*-}X$, with $D^{*-}\to {\overline{D}}^0{\pi }^{-}$, ${\overline{D}}^0\to K^{+}{\pi }^{-}$ (and charge conjugate processes). We use a data sample corresponding to $10.4{\mathrm{fb}}^{-1}$ of $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$, collected with the D0 experiment at the Fermilab Tevatron collider. We extract the charge asymmetries in these two channels as a function of the visible proper decay length of the $B^0$ meson, correct for detector-related asymmetries using data-driven methods, and account for dilution from charge-symmetric processes using Monte Carlo simulation. The final measurement combines four signal visible proper decay length regions for each channel, yielding $a_{\mathrm{sl}}^d=[0.68\pm 0.45(\mathrm{stat})\pm 0.14(\mathrm{syst})]\%$. This is the single most precise measurement of this parameter, with uncertainties smaller than the current world average of $B$ factory measurements.

• Received 30 August 2012

DOI:https://doi.org/10.1103/PhysRevD.86.072009