$CP$ asymmetries in charm decays into neutral kaons

TL;DR

This paper identifies a significant new $CP$-violation effect in charm decays into neutral kaons caused by interference and meson mixing, which can be measured at LHCb and Belle II and impacts new physics searches.

Contribution

It uncovers a previously overlooked $CP$-violation effect in charm decays involving neutral kaons, with potential implications for experimental analyses.

Findings

Estimated effect size of about 10^{-3}

Proposes measurement of time-dependent $CP$ asymmetries

Highlights importance for new physics searches

Abstract

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 $D^{+}\to\pi^{+}K_S^0$ and $D_{s}^{+}\to K^{+} K_S^0$ 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.