CP violation in the D0 -> pi+ pi- decay at CDF

We report a measurement of the \CP\ violating asymmetry in $D^0\to {\pi }^{+}{\pi }^{-}$ decays using approximately 215,000 decays reconstructed in about $5.94$ fb${}^{-1}$ of CDF data. We use the strong $D^{\star +}\to D^0{\pi }^{+}$ decay (“$D^{\star }$ tag”) to identify the flavor of the charmed meson at production time and exploit \CP-conserving strong $c\bar{c}$ pair-production in $p\bar{p}$ collisions. Higher statistic samples of Cabibbo-favored $D^0\to K^{-}{\pi }^{+}$ decays with and without $D^{\star }$ tag are used to highly suppress systematic uncertainties due to detector effects. The result, $\Acp(D^0 \to \pi^{+}\pi^{-}) = \bigl[0.22\pm0.24\stat\pm0.11\syst\bigr]%$, is the world’s most precise measurement to date and it is fully consistent with no \CP\ violation.