First Measurement of Time-Dependent CP Violation in the  \(B^{0} \rightarrow {K^{0}_\textrm{S}} {\pi ^{0}}\) Decay at Belle II

The first time-dependent analysis of the \({B ^{0} \rightarrow {K ^{0}_\textrm{S}} {\pi ^{0}}}\) decay is performed within Belle II using a sample of \(e ^+ e ^{-} \) collisions equivalent to \(189.8 \mathrm {\,fb}^{-1} \) of integrated luminosity recorded at the \(\varUpsilon (4S)\) resonance. We measure the decay branching fraction \(\mathcal {B}\) \((B ^0 \rightarrow K ^0 \pi ^{0}) = [11.0 \pm 1.2\, \mathrm {(stat)} \pm 1.0\, \mathrm {(syst)} ] \times 10^{-6}\) and direct CP violation asymmetry \(A_{CP} (B ^0 \rightarrow K ^0 \pi ^{0})= -0.41_{-0.32}^{+0.30}\, \mathrm {(stat)} \pm 0.09\, \mathrm {(syst)} \) .