Measurement of direct $CP$ violation parameters in $B^{\pm }\to J/\psi K^{\pm }$ and $B^{\pm }\to J/\psi {\pi }^{\pm }$ decays with $10.4{\mathrm{fb}}^{-1}$ of Tevatron data

We present a measurement of the direct $CP$-violating charge asymmetry in $B^{\pm }$ mesons decaying to $J/\psi K^{\pm }$ and $J/\psi {\pi }^{\pm }$ where $J/\psi$ decays to ${\mu }^{+}{\mu }^{-}$, using the full run II data set of $10.4{\mathrm{fb}}^{-1}$ of proton-antiproton collisions collected using the D0 detector at the Fermilab Tevatron Collider. A difference in the yield of $B^{-}$ and $B^{+}$ mesons in these decays is found by fitting to the difference between their reconstructed invariant mass distributions resulting in asymmetries of $A^{J/\psi K}=[0.59\pm 0.37]\%$, which is the most precise measurement to date, and $A^{J/\psi \pi }=[-4.2\pm 4.5]\%$. Both measurements are consistent with standard model predictions.

Figure 1

The polarity-weighted $J/\psi h^{\pm }$ invariant mass distribution, where the $h^{\pm }$ is assigned the charged kaon mass, after selecting on the likelihood-ratio function optimized for $A_{\mathrm{raw}}^{J/\psi K}$. The bottom panel shows the fit residuals (the error bars represent the statistical uncertainty). Fit described in the text.

Figure 2

The fit to the difference distribution for the data optimized for $A_{\mathrm{raw}}^{J/\psi K}$ (the fit is described in the text).