We search for CP violation in the decay $D^+rightarrow K^0_S K^+$ using a data sample with an integrated luminosity of 977 fb$^{-1}$ collected with the Belle detector at the KEKB $e^+e^-$ asymmetric-energy collider. No CP violation has been observed and the CP asymmetry in $D^+rightarrow K^0_S K^+$ decay is measured to be $(-0.25pm0.28pm0.14)%$, which is the most sensitive measurement to date. After subtracting CP violation due to $K^0-bar{K}^0$ mixing, the CP asymmetry in $D^+rightarrowbar{K}^0 K^+$ decay is found to be $(+0.08pm0.28pm0.14)%$.
We report a study of the decay $D^0 to K^0_S K^0_S$ using 921~fb$^{-1}$ of data collected at or near the $Upsilon(4S)$ and $Upsilon(5S)$ resonances with the Belle detector at the KEKB asymmetric energy $e^+e^-$ collider. The measured time-integrated $CP$ asymmetry is $ A_{CP}(D^0 to K^0_S K^0_S) = (-0.02 pm 1.53 pm 0.02 pm 0.17) %$, and the branching fraction is $mathcal{B} (D^{0}rightarrow K_{S}^{0}K_{S}^{0})$ = (1.321 $pm$ 0.023 $pm$ 0.036 $pm$ 0.044) $times$ 10$^{-4}$, where the first uncertainty is statistical, the second is systematic, and the third is due to the normalization mode ($D^0 to K_S^0 pi^0$). These results are significantly more precise than previous measurements available for this mode. The $A_{CP}$ measurement is consistent with the standard model expectation.
We observe evidence for CP violation in the decay $D^+rightarrow K^0_Spi^+$ using a data sample with an integrated luminosity of 977 fb$^{-1}$ collected by the Belle detector at the KEKB $e^+e^-$ asymmetric-energy collider. The CP asymmetry in the decay is measured to be $(-0.363pm0.094pm0.067)%$, which is 3.2 standard deviations away from zero, and is consistent with the expected CP violation due to the neutral kaon in the final state.
A measurement of the time-integrated $CP$ asymmetry in $D^0rightarrow K^0_S K^0_S$ decays is reported. The data correspond to an integrated luminosity of about $2$ fb$^{-1}$ collected in 2015-2016 by the LHCb collaboration in $pp$ collisions at a centre-of-mass energy of $13$ TeV. The $D^0$ candidate is required to originate from a $D^{ast +} rightarrow D^0 pi^+$ decay, allowing the determination of the flavour of the $D^0$ meson using the pion charge. The $D^0 rightarrow K^{+}K^{-}$ decay, which has a well measured $CP$ asymmetry, is used as a calibration channel. The $CP$ asymmetry for $D^0rightarrow K^0_S K^0_S$ is measured to be begin{equation*} mathcal{A}^{CP}(D^0rightarrow K^0_S K^0_S) = (4.3pm 3.4pm 1.0)%, end{equation*} where the first uncertainty is statistical and the second is systematic. This result is combined with the previous LHCb measurement at lower centre-of-mass energies to obtain begin{equation*} mathcal{A}^{CP}(D^0rightarrow K^0_S K^0_S) = (2.3pm 2.8pm 0.9)%. end{equation*}
We report a measurement of the time-integrated $CP$ asymmetry in the neutral charm meson decay $D^0 to K^0_S K^0_S$ using 921~fb$^{-1}$ data collected at the $Upsilon(4S)$ and $Upsilon(5S)$ resonances with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The observed asymmetry is $$ A_{CP}(D^0 to K^0_S K^0_S) = (-0.02 pm 1.53 pm 0.17) %, $$ where the first uncertainty is statistical and the second systematic. This latter uncertainty is dominated by the error of the normalisation channel. The result is consistent with Standard Model expectations and improves the uncertainty with respect to previous measurement of this quantity by more than a factor of three.
A model-independent search for direct CP violation in the Cabibbo suppressed decay $D^+ to K^- K^+pi^+$ in a sample of approximately 370,000 decays is carried out. The data were collected by the LHCb experiment in 2010 and correspond to an integrated luminosity of 35 pb$^{-1}$. The normalized Dalitz plot distributions for $D^+$ and $D^-$ are compared using four different binning schemes that are sensitive to different manifestations of CP violation. No evidence for CP asymmetry is found.