  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.
