2018-10-03  P7F

New CP violation in charm decays

Hsiang-nan Li

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 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 $D^{+} o pi^{+}K_S^0$ and 
$D_{s}^{+} o K^{+} K_S^0$ modes, which are accessible at the LHCb 
and Belle II. If confirmed, the new effect has to be 
taken into account, as the above direct $CP$ asymmetries are used to 
search for new physics.