A measurement of the $CP$ asymmetry in $D^0\to K_{\mathrm{S}}^0{K}_{\mathrm{S}}^0$ 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 $6{\mathrm{fb}}^{-1}$. The flavor of the $D^0$ candidate is determined using the charge of the $D^{*\pm }$ meson, from which the decay is required to originate. The $D^0\to K^{+}{K}^{-}$ decay is used as a calibration channel. The time-integrated $CP$ asymmetry for the $D^0\to K_{\mathrm{S}}^0{K}_{\mathrm{S}}^0$ mode is measured to be ${\mathcal{A}}^{CP}(D^0\to K_{\mathrm{S}}^0{K}_{\mathrm{S}}^0)=(-3.1\pm 1.2\pm 0.4\pm 0.2)$, where the first uncertainty is statistical, the second is systematic, and the third is due to the uncertainty on the $CP$ asymmetry of the calibration channel. This is the most precise determination of this quantity to date.

• Received 17 May 2021
• Accepted 1 July 2021

DOI:https://doi.org/10.1103/PhysRevD.104.L031102

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