Measurement of $CP$ asymmetry in $D^0\to K^{-}{K}^{+}$ and $D^0\to \ddot{I}{€}^{-}\ddot{I}{€}^{+}$ decays

Abstract

Time-integrated $CP$ asymmetries in $D^0$ decays to the final states $K^{-}{K}^{+}$ and $\ddot{I}{€}^{-}\ddot{I}{€}^{+}$ are measured using proton-proton collisions corresponding to $3{\mathrm{fb}}^{-1}$ of integrated luminosity collected at centre-of-mass energies of $7\mathrm{Te}\mathrm{V}$ and $8\mathrm{Te}\mathrm{V}$. The $D^0$ mesons are produced in semileptonic $b$-hadron decays, where the charge of the accompanying muon is used to determine the initial flavour of the charm meson. The difference in $CP$ asymmetries between the two final states is measured to be \begin{align} ΔA_{CP} = A_{CP}(K^-K^+)-A_{CP}(π^-π^+) = (+0.14 \pm 0.16\mathrm{\,(stat)} \pm 0.08\mathrm{\,(syst)})\% \ . \nonumber \end{align} A measurement of $A_{CP}(K^{-}{K}^{+})$ is obtained assuming negligible $CP$ violation in charm mixing and in Cabibbo-favoured $D$ decays. It is found to be \begin{align} A_{CP}(K^-K^+) = (-0.06 \pm 0.15\mathrm{\,(stat)} \pm 0.10\mathrm{\,(syst)}) \% \ ,\nonumber \end{align} where the correlation coefficient between $\hat{I}”A_{CP}$ and $A_{CP}(K^{-}{K}^{+})$ is $\ddot{I}=0.28$. By combining these results, the $CP$ asymmetry in the $D^0\to \ddot{I}{€}^{-}\ddot{I}{€}^{+}$ channel is $A_{CP}(\ddot{I}{€}^{-}\ddot{I}{€}^{+})=(-0.20\pm 0.19(\mathrm{stat})\pm 0.10(\mathrm{syst}))\%$.

19 pages, 5 figures