Measurement of 𝐶⁢𝑃 asymmetry in 𝐷0→𝐾0S⁢𝐾0S decays

A measurement of the 𝐶⁢𝑃 asymmetry in 𝐷0→𝐾0S⁢𝐾0S decays is reported, based on a data sample of proton-proton collisions collected by the LHCb experiment from 2015 to 2018, corresponding to an integrated luminosity of 6  fb−1. The flavor of the 𝐷0 candidate is determined using the charge of the 𝐷*± meson, from which the decay is required to originate. The 𝐷0→𝐾+⁢𝐾− decay is used as a calibration channel. The time-integrated 𝐶⁢𝑃 asymmetry for the 𝐷0→𝐾0
S⁢𝐾0S mode is measured to be 𝒜𝐶⁢𝑃⁡(𝐷0→𝐾0S⁢𝐾0S)=(−3.1±1.2±0.4±0.2), where the first uncertainty is statistical, the second is systematic, and the third is due to the uncertainty on the 𝐶⁢𝑃 asymmetry of the calibration channel. This is the most precise determination of this quantity to date.