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

A measurement of the time-integrated $CP$ asymmetry in the Cabibbo-suppressed decay $D^0\to K^{-}{K}^{+}$ is performed using pp collision data, corresponding to an integrated luminosity of 3fb${}^{-1}$, collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV. The flavour of the charm meson at production is determined from the charge of the pion in $D^{\ast +}\to D^0{\pi }^{+}$ and $D^{\ast -}\to \overline{D^0}{\pi }^{-}$ decays. The time-integrated $CP$ asymmetry $A_{CP}(K^{-}{K}^{+})$ is obtained assuming negligible $CP$ violation in charm mixing and in Cabibbo-favoured $D^0\to K^{-}{\pi }^{+}$, $D^{+}\to K^{-}{\pi }^{+}{\pi }^{+}$ and $D^+\rightarrow \bar{K^0}\pi^+$decaysusedascalibrationchannels\mathrm{.}Itisfoundtobe$A_{CP}(K^-K^+)=(0.14\pm0.15(stat)\pm0.10(syst))%$. A combination of this result with previous LHCb measurements yields $A_{CP}(K^{-}{K}^{+})=(0.04\pm 0.12(stat)\pm 0.10(syst))\mathrm{\%}$, $A_{CP}({\pi }^{-}{\pi }^{+})=(0.07\pm 0.14(stat)\pm 0.11(syst))\mathrm{\%}$. These are the most precise measurements from a single experiment. The result for $A_{CP}(K^{-}{K}^{+})$ is the most precise determination of a time-integrated $CP$ asymmetry in the charm sector to date, and neither measurement shows evidence of CP asymmetry.