Measurement of the time-integrated CP asymmetry in $D^0\to K_S^0{K}_S^0$ decays using Belle and Belle II data

We measure the time-integrated CP asymmetry in $D^0\to K_S^0{K}_S^0$ decays reconstructed in $e^{+}{e}^{-}\to c\bar{c}$ events collected by the Belle and Belle II experiments. The corresponding data samples have integrated luminosities of 980 fb${}^{-1}$ and 428 fb${}^{-1}$, respectively. The $D^0$ decays are required to originate from the $D^{\ast +}\to D^0{\pi }^{+}$ decay, which determines the charm flavor at production time. A control sample of $D^0\to K^{+}{K}^{-}$ decays is used to correct for production and detection asymmetries. The result, $(-1.4\pm 1.3(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t})\pm 0.1(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}))\mathrm{\%}$, is consistent with previous determinations and with CP symmetry.