  In top-pair events where at least one of the tops decays semi-leptonically,
the identification of the lepton charge allows to tag not only the top charge
but also that of the subsequent b quark. In cases where the b also decays
semi-leptonically, the charge of the two leptons can be used to probe CP
violation in heavy flavor mixing and decays. This strategy to measure CP
violation is independent of those adopted so far in experiments, and can
already constrain non Standard Model sources of CP violation with current and
near future LHC data. To demonstrate the potential of this method we construct
two CP asymmetries based on same-sign and opposite-sign leptons and estimate
their sensitivities. This proposal opens a new window for doing precision
measurements of CP violation in b and c quark physics via high p_T processes at
ATLAS and CMS.
