Abstract
A measurement of the time-integrated $CP$ asymmetry in the Cabibbo-suppressed decay $D^0\rightarrow K^-K^+$ 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 $D^0\rightarrow K^-\pi^+$, $D^+\rightarrow K^-\pi^+\pi^+$ and $D^+\rightarrow \bar{K^0}\pi^+$ decays used as calibration channels. It is found to be $A_{CP}(K^-K^+)=(0.14\pm0.15(stat)\pm0.10(syst))\%$. A combination of this result with previous LHCb measurements yields $A_{CP}(K^-K^+)=(0.04\pm0.12(stat)\pm0.10(syst))\%$, $A_{CP}(\pi^-\pi^+)=(0.07\pm0.14(stat)\pm0.11(syst))\%$. 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.
Highlights
In the Standard Model (SM), the violation of the charge-parity (CP) symmetry is governed by an irreducible complex phase in the Cabibbo–Kobayashi–Maskawa (CKM) matrix
Recent studies of CP violation in weak decays of D mesons have not shown evidence of CP symmetry breaking [1], while its violation is well established in decays of mesons with down-type quarks [2,3,4,5,6]
These regions occur because low momentum particles of one charge at large or small angles in the horizontal plane may be deflected either out of the detector acceptance or into the non-instrumented beam pipe region, whereas particles with the other charge are more likely to remain within the acceptance
Summary
In the Standard Model (SM), the violation of the charge-parity (CP) symmetry is governed by an irreducible complex phase in the Cabibbo–Kobayashi–Maskawa (CKM) matrix. The remaining production asymmetry of the D+ meson A P (D+), and the detection asymmetry of the other pion πh+ are eliminated by incorporating the Cabibbo-favoured decay D+ → K 0π + in the measurement. The detection asymmetry A D (K 0) includes CP violation, mixing and different cross-sections for the interaction of neutral kaons with the detector material. All of these effects are known, and A D (K 0) is calculated to be small since only neutral kaons that decay within the first part of the detector are selected [18].
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