Measurement of the $CP$ Violation Parameter $\cal{A}_{\Gamma}$ in Two-Body Charm Decays

We present a study of indirect $CP$ violation in $D^0$ mesons through the parameter $\cal{A}_{\Gamma}$. This parameter is defined as the asymmetry of lifetimes measured in decays of $D^0$ and $\bar{D}^0$ mesons to the $CP$ eigenstate $K^{+}K^{-}$. The measurement is performed using absolute lifetime measurements exploiting a data-driven technique to correct for lifetime biasing effects. The result on data collected in 2010, equivalent to 28 $\pm$ 3 pb$^{-1}$, is \begin{align} \cal{A}_{\Gamma} = (-5.9 \pm 5.9_{stat} \pm 2.1_{syst}) x 10^{-3}. \end{align}