A search for time-integrated CP violation in $D^0 \to h^-h^+$ decays

The preliminary results of a search for time-integrated CP violation in $D^0 \to h^-h^+$ ($h=K$, $\pi$) decays performed with 580~pb$^-1$ of data collected by LHCb in 2011 are presented. The flavour of the charm meson is determined by the charge of the slow pion in the $D^{*+} \to D^0 \pi^+$ and $D^{*-} \to \bar{D}^0 \pi^-$ decay chains. The difference in CP asymmetry between $D^0 \to K^- K^+$ and $D^0 \to \pi^- \pi^+$, $\Delta A_{CP} \equiv A_{CP}(K^-K^+) \, - \, A_{CP}(\pi^-\pi^+)$, is measured to be $\Delta A_{CP} = \left[ -0.82 \pm 0.21 (\mathrm{stat.}) \pm 0.11 (\mathrm{syst.}) \right]\%$. This differs from the hypothesis of CP conservation by $3.5\sigma$.