Search for the decay of a $B^0$ or ${\overline{B}}^0$ meson to ${\overline{K}}^{*0}{K}^0$ or $K^{*0}{\overline{K}}^0$

We present a search for the decay of a $B^0$ or ${\overline{B}}^0$ meson to a ${\overline{K}}^{*0}{K}^0$ or $K^{*0}{\overline{K}}^0$ final state, using a sample of approximately $232\times {10}^6$ $B\overline{B}$ events collected with the BABAR detector at the PEP-II asymmetric energy $e^{+}{e}^{-}$ collider at SLAC. The measured branching fraction is $\mathcal{B}(B^0\to {\overline{K}}^{*0}{K}^0)+\mathcal{B}(B^0\to K^{*0}{\overline{K}}^0)=({0.2}_{-0.8-0.3}^{+0.9+0.1})\times {10}^{-6}$. We obtain the following upper limit for the branching fraction at 90% confidence level: $\mathcal{B}(B^0\to {\overline{K}}^{*0}{K}^0)+\mathcal{B}(B^0\to K^{*0}{\overline{K}}^0)<1.9\times {10}^{-6}$. We use our result to constrain the standard model prediction for the deviation of the $CP$ asymmetry in $B^0\to \varphi K^0$ from $\sin 2\beta$.

Figure 1

Feynman diagrams for ${\overline{B}}^0\to K^{*0}{\overline{K}}^0$.

Figure 2

Distributions of $\Delta E$, $m_{\mathrm{ES}}$, and $M_{K^{+}{\pi }^{-}}$. The points with uncertainties show the data. The curves show projections of the ML fit. A selection requirement on the likelihood ratio has been applied as described in the text. The solid curve shows the sum of all fitted components, including the signal. The dashed curve shows the sum of all background components. The dotted curve (barely visible) shows the signal component.