Measurement of the direct $CP$ violating charge asymmetry in $B^{\pm }\to {\mu }^{\pm }{\nu }_{\mu }{D}^0$ decays

We present the first measurement of the $CP$ violating charge asymmetry in $B^{\pm }\to {\mu }^{\pm }{\nu }_{\mu }{D}^0$ decays using the full Run II integrated luminosity of $10.4{\mathrm{fb}}^{-1}$ in proton-antiproton collisions collected with the D0 detector at the Fermilab Tevatron Collider. We measure a difference in the yield of $B^{-}$ and $B^{+}$ mesons in these decays by fitting the reconstructed invariant mass distributions. This results in an asymmetry of $A^{\mu D^0}=[-0.14\pm 0.20]\%$, which is consistent with standard model predictions.

Figure 1

The sum of the $K^{+}{\pi }^{-}$ and $K^{-}{\pi }^{+}$ invariant mass distributions for selected $\mu D^0$ candidates. The curve shows the result of the fit described in the text.

Figure 2

The results of a fit to the differences between the numbers of ${\mu }^{-}{D}^0$ and ${\mu }^{+}{\overline{D}}^0$ events as function of the $K\pi$ mass.