We observe $D^0-bar{D}^0$ mixing in the decay $D^0rightarrow K^+pi^-$ using a data sample of integrated luminosity 976 fb$^{-1}$ collected with the Belle detector at the KEKB $e^+e^-$ asymmetric-energy collider. We measure the mixing parameters ${x}^
2 = (0.09pm0.22)times 10^{-3}$ and $y = (4.6pm3.4)times 10^{-3}$ and the ratio of doubly Cabibbo-suppressed to Cabibbo-favored decay rates $R_D = (3.53pm0.13)times 10^{-3}$, where the uncertainties are statistical and systematic combined. Our measurement excludes the no-mixing hypothesis at the 5.1 standard deviation level.
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 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 de
cay 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.
We review basic phenomenology on $D^0$ mixing/CP violation and recent experimental results on them. $D^0$ mixing is established by combining results from multiple experiments but no CP violation in the charm sector has been seen. $D^0$ mixing from a
single experiment will clarify the size of the mixing, and observation of CP violation in charm decays at the present level of experimental sensitivity would be clear signal of new physics beyond the standard model.
We have searched for CP violation in the charmed meson decays $D^{+}_{(s)}to K^0_Spi^+$ and $D^{+}_{(s)}to K^0_S K^+$ using 673 fb$^{-1}$ of data collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. No evidence for CP vi
olation is observed. We report the most sensitive CP asymmetry measurements to date for these decays: $A_{CP}^{D^+to K^0_Spi^+}=(-0.71pm0.19pm0.20)%$, $A_{CP}^{D^+_sto K^0_Spi^+}=(+5.45pm2.50pm0.33)%$, $A_{CP}^{D^+to K^0_S K^+}=(-0.16pm0.58pm0.25)%$, and $A_{CP}^{D^+_sto K^0_S K^+}=(+0.12pm0.36pm0.22)%$, where the first uncertainties are statistical and the second are systematic.
We report the first observation of the doubly Cabibbo-suppressed decay $D^+_sto K^+K^+pi^-$ using 605 fb$^{-1}$ of data collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The branching ratio with respect to its Cabibbo
-favored counterpart $mathcal{B}(D^+_sto K^+K^+pi^-)$ / $mathcal{B}(D^+_sto K^+K^-pi^+)$ is (0.229$pm0.028pm$0.012)%, where the first uncertainty is statistical and the second is systematic. We also report a significantly improved measurement of the doubly Cabibbo-suppressed decay $D^+to K^+pi^+pi^-$, with a branching ratio $mathcal{B}(D^+to K^+pi^+pi^-)$ / $mathcal{B}(D^+to K^-pi^+pi^+)$=(0.569$pm0.018pm$0.014)%.
