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

Abstract

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 $D^{+}\to \overline{K^0}{\pi }^{+}$ decays used as calibration channels. It is found to be $A_{CP}(K^{-}{K}^{+})=(0.14\pm 0.15(stat)\pm 0.10(syst))\%$. A combination of this result with previous LHCb measurements yields $A_{CP}(K^{-}{K}^{+})=(0.04\pm 0.12(stat)\pm 0.10(syst))\%$, $A_{CP}({\pi }^{-}{\pi }^{+})=(0.07\pm 0.14(stat)\pm 0.11(syst))\%$. 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.

All figures and tables, along with any supplementary material and additional information, are available at https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2016-035.html

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