New results on CP violation in the charm sector

The difference in CP violation between the $D^0 \to K^+K^–$ and $D^0 \to \mu^+ \mu^-$ decays ($\Delta A_{CP}$) has emerged as an interesting observable to search for matter-antimatter asymmetries in the charm sector. By taking the difference between the two modes, most of the asymmetries induced by the detector or coming from the production mechanism cancel. A previous LHCb measurement, using 0.6 fb$^{–1}$ of data, gave 3.5$\sigma$ evidence for CP violation in the charm sector, which was further strengthened by results from the CDF and Belle collaborations. We present an update of the $\Delta A_{CP}$ measurement, consisting of two independent analyses, both using the full 2011 data set of 1.0 fb$^{–1}$. In the first, the initial flavour of the D meson ($D^0$ or $\bar{D^0}$) is inferred from the charge of the slow pion in the decay $D^{*+} \to D^0 \mu^+$, as in the previous publication. The second uses D mesons produced in semileptonic B decays, where the charge of the associated muon provides the tag.