Evidence for $B^{+}\to {\overline{K}}^0{K}^{+}$ and $B^0\to K^0{\overline{K}}^0$, and Measurement of the Branching Fraction and Search for Direct $CP$ Violation in $B^{+}\to K^0{\pi }^{+}$

We present evidence for the $b\to d$ penguin-dominated decays $B^{+}\to {\overline{K}}^0{K}^{+}$ and $B^0\to K^0{\overline{K}}^0$ in $227\times {10}^6$ ${\rm Y}(4S)\to B\overline{B}$ decays collected with the BABAR detector. We measure the branching fractions $\mathcal{B}(B^{+}\to {\overline{K}}^0{K}^{+})=(1.5\pm 0.5\pm 0.1)\times {10}^{-6}(<2.4\times {10}^{-6})$ and $\mathcal{B}(B^0\to K^0{\overline{K}}^0)=({1.19}_{-0.35}^{+0.40}\pm 0.13)\times {10}^{-6}$, where the uncertainties are statistical and systematic, respectively. We also present improved measurements of the charge-averaged branching fraction $\mathcal{B}(B^{+}\to K^0{\pi }^{+})=(26.0\pm 1.3\pm 1.0)\times {10}^{-6}$ and $CP$-violating charge asymmetry ${\mathcal{A}}_{CP}(K^0{\pi }^{+})=-0.09\pm 0.05\pm 0.01$, where the uncertainties are statistical and systematic, respectively.

Figure 1

Distributions of (a) $m_{\mathrm{ES}}$ and (b) $\Delta E$ for signal (main plot) and background (inset) $B^{+}\to K_S^0{\pi }^{+}$ candidates (points with error bars) using the weighting technique described in the text. Solid curves represent the corresponding PDFs used in the fit. In (c)–(f) we show projections of $m_{\mathrm{ES}}$ and $\Delta E$ for $K_S^0{K}^{+}$ (c), (d) and $K_S^0{K}_S^0$ (e), (f) decays (points with error bars) enhanced in signal decays using additional requirements on probability ratios. Solid curves represent the PDF projections for the sum of signal and background components, while the dotted curves show the contribution from background only.