Measurement of the time-integrated $CP$ asymmetry in $D^0 \to K^0_S K^0_S$ decays

TL;DR

This paper reports a precise measurement of the $CP$ asymmetry in $D^0 o K^0_S K^0_S$ decays using LHCb data, finding results consistent with the Standard Model and significantly reducing uncertainty compared to previous measurements.

Contribution

The study provides the most precise measurement to date of the $CP$ asymmetry in this decay mode, improving the uncertainty by over a factor of three.

Findings

Measured $A_{CP} = -0.029 \, ext{with uncertainties}$

Result consistent with Standard Model predictions

Significantly reduced measurement uncertainty

Abstract

The time-integrated $CP$ asymmetry in the decay $D^0 \to K^0_S K^0_S$ is measured using $3 fb^{-1}$ of proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The flavour of the $D^0$ meson is determined by use of the decay $D^{*+} \to D^0 \pi^+$ and its charge conjugate mode. The result is \[ {\cal A}_{CP} = -0.029 \pm 0.052 \pm 0.022, \] where the first uncertainty is statistical and the second systematic. The result is consistent with Standard Model expectations and improves the uncertainty with respect to the only previous measurement of this quantity by more than a factor of three.