Observation of $B_s^0\to J/\psi K^{*}(892{)}^0$ and $B_s^0\to J/\psi K_S^0$ decays

We report the first observation of two Cabibbo-suppressed decay modes of the $B_s^0$ meson. Using a sample of $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ corresponding to $5.9{\mathrm{fb}}^{-1}$ of integrated luminosity collected with the CDF II, the collider detector at the Fermilab Tevatron, we search for new $B_s^0$ decay modes in a sample of events containing $J/\psi \to {\mu }^{+}{\mu }^{-}$ decays. We reconstruct a $B_s^0\to J/\psi K^{*}(892{)}^0$ signal with $K^{*}(892{)}^0\to K^{+}{\pi }^{-}$, observing a yield of $151\pm 25$ events with a statistical significance of $8.0\sigma$. We also reconstruct a $B_s^0\to J/\psi K_S^0$ signal with $K_S^0\to {\pi }^{+}{\pi }^{-}$, observing a yield of $64\pm 14$ events with a statistical significance of $7.2\sigma$. From these yields, we extract the branching ratios $\mathcal{B}(B_s^0\to J/\psi K^{*}(892{)}^0)=(8.3\pm 3.8)\times {10}^{-5}$ and $\mathcal{B}(B_s^0\to J/\psi K^0)=(3.5\pm 0.8)\times {10}^{-5}$, where statistical, systematic, and fragmentation-fraction uncertainties are included in the combined uncertainty.

Figure 1

(a) Invariant mass distribution in data for $J/\psi K^{*0}$ candidates and fit including the different contributions. (b) We enlarge the distribution in the signal region for more detail.

Figure 2

(a) NN response where the solid line is signal simulation and the dashed one is sideband data. (b) Figure of merit $S/(1.5+\sqrt{B})$ as a function of NN response. The vertical line indicates the optimized cut in the NN response.

Figure 3

(a) Invariant mass distribution in data for $J/\psi K_S^0$ candidates and fit including the different contributions. (b) We enlarge the distribution in the signal region for more detail.