The semileptonic $CP$ asymmetry in $B^0$-${\overline{B}}^0$ mixing, $a_{\text{sl}}^d$, is measured in proton-proton collision data, corresponding to an integrated luminosity of $3.0{\mathrm{fb}}^{-1}$, recorded by the LHCb experiment. Semileptonic $B^0$ decays are reconstructed in the inclusive final states $D^{-}{\mu }^{+}$ and $D^{*-}{\mu }^{+}$, where the $D^{-}$ meson decays into the $K^{+}{\pi }^{-}{\pi }^{-}$ final state and the $D^{*-}$ meson into the ${\overline{D}}^0(\to K^{+}{\pi }^{-}){\pi }^{-}$ final state. The asymmetry between the numbers of $D^{(*)-}{\mu }^{+}$ and $D^{(*)+}{\mu }^{-}$ decays is measured as a function of the decay time of the $B^0$ mesons. The $CP$ asymmetry is measured to be $a_{\text{sl}}^d=(-0.02\pm 0.19\pm 0.30)\%$, where the first uncertainty is statistical and the second systematic. This is the most precise measurement of $a_{\text{sl}}^d$ to date and is consistent with the prediction from the standard model.

• Received 1 October 2014

DOI:https://doi.org/10.1103/PhysRevLett.114.041601

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© 2015 CERN, for the LHCb Collaboration