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

Understand

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.