Measurement of CP asymmetries in $B^0\to K^0{\pi }^0$ decays

Abstract

We report measurements of CP violation parameters in $B^0\to K^0{\pi }^0$ decays based on a data sample of $657\times 10^{6}B\bar{B}$ pairs collected with the Belle detector at the KEKB $e^{+}{e}^{-}$ asymmetric-energy collider. We use $B^0\to K_S^0{\pi }^0$ decays for both mixing-induced and direct $CP$ violating asymmetry measurements and $B^0\to K_L^0{\pi }^0$ decays for the direct CP violation measurement. The CP violation parameters obtained are $\sin 2{\varphi }_1^{\mathrm{eff}}=+0.67\pm 0.31(stat)\pm 0.08(syst)$ and ${\mathcal{A}}_{K^0{\pi }^0}=+0.14\pm 0.13(stat)\pm 0.06(syst)$. The branching fraction of $B^0\to K^0{\pi }^0$ decay is measured to be $\mathcal{B}(B^0\to K^0{\pi }^0)=(8.7\pm 0.5(stat.)\pm 0.6(syst.))\times 10^{-6}$. The observed ${\mathcal{A}}_{K^0{\pi }^0}$ value differs by 1.9 standard deviations from the value expected from an isospin sum rule.

6 pages, 3 figures

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