A measurement of the time-integrated $CP$ asymmetry in the Cabibbo-suppressed decay $D^0rightarrow K^-K^+$ 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 $D^{*+}rightarrow D^0 pi^+$ and $D^{*-}rightarrow bar{D^0} pi^-$ decays. The time-integrated $CP$ asymmetry $A_{CP}(K^-K^+)$ is obtained assuming negligible $CP$ violation in charm mixing and in Cabibbo-favoured $D^0rightarrow K^-pi^+$, $D^+rightarrow K^-pi^+pi^+$ and $D^+rightarrow bar{K^0}pi^+$ decays used as calibration channels. It is found to be $A_{CP}(K^-K^+)=(0.14pm0.15(stat)pm0.10(syst))%$. A combination of this result with previous LHCb measurements yields $A_{CP}(K^-K^+)=(0.04pm0.12(stat)pm0.10(syst))%$, $A_{CP}(pi^-pi^+)=(0.07pm0.14(stat)pm0.11(syst))%$. 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.
تحميل البحث