Direct CP violation in charm at Belle
22 Aug 2013-Vol. 174, pp 353
TL;DR: In this article, the authors used the Belle detector at the KEKB asymmetric-energy collider to search for CP violation of charmed mesons in $D^+\rightarrow K^0_S\pi+$ and $D$0/rightarrow h^+h^-$ decays, where $h$ denotes $K$ and $\pi$.
Abstract: Using the full data sample collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider, we have searched for CP violation of charmed mesons in $D^+\rightarrow K^0_S\pi^+$ and $D^0\rightarrow h^+h^-$ decays, where $h$ denotes $K$ and $\pi$. We observe evidence for CP violation in $D^+\rightarrow K^0_S\pi^+$ decay with 3.2 standard deviations away from zero, $(-0.363\pm0.094\pm0.067)%$, while the asymmetry is consistent with the expected CP violation due to the neutral kaon in the final state. No evidence for CP violation in $D^0\rightarrow h^+h^-$ is observed with $A^{KK}_{CP}=(-0.32\pm0.21\pm0.09)%$ and $A^{\pi\pi}_{CP}=(+0.55\pm0.36\pm0.09)%$. The CP asymmetry difference between $D^0\rightarrow K^+K^-$ and $D^0\rightarrow\pi^+\pi^-$ decays is also measured with $\Delta A^{hh}_{CP}=(-0.87\pm0.41\pm0.06)%$, which is 2.1 standard deviations away from zero and supports recent LHCb and CDF measurements.
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TL;DR: In this paper, a search for CP violation in Cabibbo-suppressed decays is performed using collision data, corresponding to an integrated luminosity of 3~fb$^{-1}, recorded by the LHCb experiment.
Abstract: A search for \CP violation in Cabibbo-suppressed $D^{\pm}\rightarrow K^0_{\mathrm{S}} K^{\pm}$ and $D^{\pm}_{s}\rightarrow K^0_{\mathrm{S}} \pi^{\pm}$ decays is performed using $pp$ collision data, corresponding to an integrated luminosity of 3~fb$^{-1}$, recorded by the LHCb experiment. The individual $CP$-violating asymmetries are measured to be \begin{eqnarray*}
\mathcal{A}_{CP}^{D^{\pm}\rightarrow K^0_{\mathrm{S}} K^{\pm}} & = & (+0.03 \pm 0.17 \pm 0.14) \%
\mathcal{A}_{CP}^{D^{\pm}_{s}\rightarrow K^0_{\mathrm{S}} \pi^{\pm}} & = & (+0.38 \pm 0.46 \pm 0.17) \%, \end{eqnarray*} assuming that $CP$ violation in the Cabibbo-favoured decays is negligible. A combination of the measured asymmetries for the four decay modes $D^{\pm}_{(s)}\rightarrow K^0_{\mathrm{S}} K^{\pm}$ and $D^{\pm}_{(s)}\rightarrow K^0_{\mathrm{S}} \pi^{\pm}$ gives the sum \[
\mathcal{A}_{CP}^{D^{\pm}\rightarrow K^0_{\mathrm{S}} K^{\pm}} + \mathcal{A}_{CP}^{D^{\pm}_{s}\rightarrow K^0_{\mathrm{S}} \pi^{\pm}} = (+0.41 \pm 0.49 \pm 0.26) \%. \] In all cases, the first uncertainties are statistical and the second systematic. The results represent the most precise measurements of these asymmetries to date and show no evidence for CP violation.
196 citations
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Abstract: The time-integrated $CP$ asymmetry in the decay $D^0 \to K^0_S K^0_S$ is measured using $3 fb^{-1}$ of proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The flavour of the $D^0$ meson is determined by use of the decay $D^{*+} \to D^0 \pi^+$ and its charge conjugate mode. The result is \[ {\cal A}_{CP} = -0.029 \pm 0.052 \pm 0.022, \] where the first uncertainty is statistical and the second systematic. The result is consistent with Standard Model expectations and improves the uncertainty with respect to the only previous measurement of this quantity by more than a factor of three.
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