Observation of the decay $B_s^0\to K^0{\overline{K}}^0$

Abstract

We measure the decay $B_s^0\to K^0{\overline{K}}^0$ using data collected at the ${\rm Y}(5S)$ resonance with the Belle detector at the KEKB $e^{+}{e}^{-}$ collider. The data sample used corresponds to an integrated luminosity of 121.4 $\mathrm{f}{\mathrm{b}}^{-1}$. We measure a branching fraction $\mathcal{B}(B_s^0\to K^0{\overline{K}}^0)=[19.6{}_{-5.1}^{+5.8}(stat.)\pm 1.0(sys.)\pm 2.0(N_{B_s^0{\overline{B}}_s^0}^{})]\times 10^{-6}$ with a significance of 5.1 standard deviations. This measurement constitutes the first observation of this decay.

6 pages, 3 figures