Measurement of the branching fraction and the $CP$-violating asymmetry for the decay $B^0\to K_S^0{\pi }^0$

We measure the branching fraction and the $CP$-violating asymmetry of $B^0\to K_S^0{\pi }^0$ decays with $227$ million ${\rm Y}(4S)\to B\overline{B}$ events collected with the BABAR detector at the PEP-II asymmetric-energy $e^{+}{e}^{-}$ collider at SLAC. We obtain a branching fraction $\mathcal{B}(B^0\to K^0{\pi }^0)=(11.4\pm 0.9\pm 0.6)\times {10}^{-6}$ and $CP$-violating asymmetry parameters $C_{K_S^0}{\pi }^0=0.06\pm 0.18\pm 0.03$ and $S_{K_S^0}{\pi }^0={0.35}_{-0.33}^{+0.30}\pm 0.04$, where the first error is statistical and the second systematic.

Figure 1

Signal and background (inset) distributions, obtained with the weighting technique described in the text, for $m_B$ (a) and $m_{\mathrm{miss}}$ (b), $\cos {\theta }_B^{*}$ (c) and $L_2/L_0$ (d). The curves represent the PDFs used in the fit and are normalized to the fitted yield.

Figure 2

Signal distribution for $\Delta t$, obtained with the weighting technique described in the text, with $B_{\mathrm{tag}}$ tagged as $B^0$ (top) or ${\overline{B}}^0$ (center), and the asymmetry ${\mathcal{A}}_{K_S^0}{\pi }^0(\Delta t)$ (bottom). The curves represent the PDFs for signal decays in the likelihood fit.