Measurement of the Difference in $CP$-Violating Asymmetries in $D^0\to K^{+}{K}^{-}$ and $D^0\to {\pi }^{+}{\pi }^{-}$ Decays at CDF

We report a measurement of the difference ($\Delta A_{CP}$) between time-integrated $CP$-violating asymmetries in $D^0\to K^{+}{K}^{-}$ and $D^0\to {\pi }^{+}{\pi }^{-}$ decays reconstructed in the full data set of proton-antiproton collisions collected by the Collider Detector at Fermilab, corresponding to $9.7{\mathrm{fb}}^{-1}$ of integrated luminosity. The strong decay $D^{*+}\to D^0{\pi }^{+}$ is used to identify the charm meson at production as $D^0$ or ${\overline{D}}^0$. We measure $\Delta A_{CP}=[-0.62\pm 0.21(\mathrm{stat})\pm 0.10(\mathrm{syst})]\%$, which differs from zero by 2.7 Gaussian standard deviations. This result supports similar evidence for $CP$ violation in charm-quark decays obtained in proton-proton collisions.

Figure 1

Distributions of $D^0{\pi }^{+}$ mass with fit results overlaid for (a) $D^0\to {\pi }^{+}{\pi }^{-}$ decays, (b) ${\overline{D}}^0\to {\pi }^{+}{\pi }^{-}$ decays, (c) $D^0\to K^{+}{K}^{-}$ decays, and (d) ${\overline{D}}^0\to K^{+}{K}^{-}$ decays.