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

The time-integrated CP asymmetry in the decay D0→K0SK0S is measured using 3fb−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 D0 meson is determined by use of the decay D∗+→D0π+ and its charge conjugate mode. The result is ACP=−0.029±0.052±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.