Measurements of Branching Fractions and $CP$-Violating Asymmetries in $B$ Meson Decays to Charmless Two-Body States Containing a $K^0$

We present measurements of branching fractions and $CP$-violating asymmetries in decays of $B$ mesons to two-body final states containing a $K^0$. The results are based on a data sample of approximately $88\times {10}^6$ ${\rm Y}(4S)\to B\overline{B}$ decays collected with the BABAR detector at the PEP-II asymmetric-energy $B$ Factory at SLAC. We measure $\mathcal{B}(B^{+}\to K^0{\pi }^{+})=(22.3\pm 1.7\pm 1.1)\times {10}^{-6}$, $\mathcal{B}(B^0\to K^0{\pi }^0)=(11.4\pm 1.7\pm 0.8)\times {10}^{-6}$, $\mathcal{B}(B^{+}\to {\overline{K}}^0{K}^{+})<2.5\times {10}^{-6}$, and $\mathcal{B}(B^0\to K^0{\overline{K}}^0)<1.8\times {10}^{-6}$, where the first uncertainty is statistical and the second is systematic, and the upper limits are at the $90\%$ confidence level. In addition, the following $CP$-violating asymmetries have been measured: ${\mathcal{A}}_{CP}(B^{+}\to K^0{\pi }^{+})=-0.05\pm 0.08\pm 0.01$ and ${\mathcal{A}}_{CP}(B^0\to K^0{\pi }^0)=0.03\pm 0.36\pm 0.11$.

Figure 1

Distributions of $m_{\mathrm{ES}}$ and $\Delta E$ for (a),(b) $B^{+}\to K^0{\pi }^{+}$ and (c),(d) $B^0\to K^0{\pi }^0$ candidates that satisfy an optimized requirement on the signal probability, based on all the variables except the one being plotted. The solid curves are projections of the fit, while the dashed curves show the background contribution.