First decay-time-dependent analysis of $B^0\to K_S^0{\pi }^0$ at Belle II

We report measurements of the branching fraction ($\mathcal{B}$) and direct $CP$-violating asymmetry ($A_{CP}$) of the charmless decay $B^0\to K^0{\pi }^0$ at Belle II. A sample of $e^{+}{e}^{-}$ collisions, corresponding to $189.8f{b}^{-1}$ of integrated luminosity, recorded at the $\mathrm{{\rm Y}}(4S)$ resonance is used for the first decay-time-dependent analysis of these decays within the experiment. We reconstruct about 135 signal candidates, and measure $\mathcal{B}(B^0\to K^0{\pi }^0)=[11.0\pm 1.2(stat)\pm 1.0(syst)]\times {10}^{-6}$ and $A_{CP}(B^0\to K^0{\pi }^0)=-0.41_{-0.32}^{+0.30}(stat)\pm 0.09(syst)$.