Enhanced Charm CP Asymmetries from Final State Interactions

We show that final state interactions (FSI) within a CPT invariant two-channel framework can enhance the charge-parity (CP) violation difference between D^{0}→π^{-}π^{+} and D^{0}→K^{-}K^{+} decays up to the current experimental value. This result relies upon (i) the dominant tree level diagram, (ii) the well-known experimental values for the D^{0}→π^{-}π^{+} and D^{0}→K^{-}K^{+} branching ratios, and (iii) the ππ→ππ and ππ→KK scattering data to extract the strong phase difference and inelasticity. Based on well-grounded theoretical properties, we find the sign and bulk value of the ΔA_{CP} and A_{CP}(D^{0}→π^{-}π^{+}) recently observed by the LHCb Collaboration.

CP Asymmetries in Charm Decays into Neutral Kaons

We find a new CP-violation effect in charm decays into neutral kaons, which results from the interference between two tree (Cabibbo-favored and doubly Cabibbo-suppressed) amplitudes with the mixing of final-state mesons. This effect, estimated to be of an order of 10^{-3}, is much larger than the direct CP asymmetries in these decays, but missed in the literature. It can be revealed by measuring the difference of the time-dependent CP asymmetries in the D^{+}→π^{+}K_{S}^{0} and D_{s}^{+}→K^{+}K_{S}^{0} modes, which are accessible at the LHCb and Belle II experiments. If confirmed, the new effect has to be taken into account, as the above direct CP asymmetries are used to search for new physics.