Searches for CP violation in two-body charm decays

TL;DR

This paper reports on LHCb's search for CP violation in two-body charm decays, providing the most precise measurements to date and finding no significant evidence of CP violation.

Contribution

The study presents the first precise measurements of CP asymmetries in specific D0 decays using LHCb data, improving constraints on CP violation in the charm sector.

Findings

No evidence of CP violation was observed in the studied decays.

The measurement of $A_{CP}(D^0 ightarrow K_S^0 K_S^0)$ is significantly more precise than previous results.

Constraints on direct and indirect CP violation in the D0 system are tightened.

Abstract

The LHCb experiment recorded data corresponding to an integrated luminosity of 3.0 $fb^{-1}$ during its first run of data taking. These data yield the largest samples of charmed hadrons in the world and are used to search for CP violation in the $D^0$ system. Among the many measurements performed at LHCb, a measurement of the direct CP asymmetry in $D^0 \rightarrow K_S^0 K_S^0$ decays is presented and is found to be $A_{CP}(D^0 \rightarrow K_S^0 K_S^0) = (-2.9 \pm 5.2 \pm 2.2)\, \%, $ where the first uncertainty is statistical and the second systematic. This represents a significant improvement in precision over the previous measurement of this parameter. Measurements of the parameter $A^\Gamma$, defined as the CP asymmetry of the $D^0$ effective lifetime when decaying to a CP eigenstate, are also presented. Using semi-leptonic b-hadron decays to tag the flavour of the $D^0$ meson at production with the $K^+K^-$ and $\pi^+\pi^-$ final states yields $A^\Gamma(K^+K^-) = (-0.134 \pm 0.077^{+0.026}_{-0.034})\, \%,$ $A^\Gamma(\pi^+\pi^-) = (-0.092 \pm 0.145^{+0.025}_{-0.033})\, \%. $ Thus no evidence of direct or indirect CP violation in the $D^0$ system is found, though it is tightly constrained.