Measurement of the branching fraction of the decay $B_s^0\to K_{\mathrm{S}}^0{K}_{\mathrm{S}}^0$

A measurement of the branching fraction of the decay $B_s^0\to K_{\mathrm{S}}^0{K}_{\mathrm{S}}^0$ is performed using proton–proton collision data corresponding to an integrated luminosity of $5{\mathrm{fb}}^{-1}$ collected by the LHCb experiment between 2011 and 2016. The branching fraction is determined to be $\mathcal{B}(B_s^0\to K_{\mathrm{S}}^0{K}_{\mathrm{S}}^0)=[8.3\pm 1.6(\mathrm{stat})\pm 0.9(\mathrm{syst})\pm 0.8(\mathrm{norm})\pm 0.3(f_s/f_d)]\times {10}^{-6}$, where the first uncertainty is statistical, the second is systematic, and the third and fourth are due to uncertainties on the branching fraction of the normalization mode $B^0\to \varphi K_{\mathrm{S}}^0$ and the ratio of hadronization fractions $f_s/f_d$. This is the most precise measurement of this branching fraction to date. Furthermore, a measurement of the branching fraction of the decay $B^0\to K_{\mathrm{S}}^0{K}_{\mathrm{S}}^0$ is performed relative to that of the $B_s^0\to K_{\mathrm{S}}^0{K}_{\mathrm{S}}^0$ channel, and is found to be $\frac{\mathcal{B}(B^0\to K_{\mathrm{S}}^0{K}_{\mathrm{S}}^0)}{\mathcal{B}(B_s^0\to K_{\mathrm{S}}^0{K}_{\mathrm{S}}^0)}=[7.5\pm 3.1(\mathrm{stat})\pm 0.5(\mathrm{syst})\pm 0.3(f_s/f_d)]\times {10}^{-2}$.

Figure 1

Fits to the invariant-mass distribution $m(K_{\mathrm{S}}^0{K}^{+}{K}^{-})$ of the normalization decay channel. The black curve represents the complete model, the $B^0\to \varphi K_{\mathrm{S}}^0$ component is given in green (dashed), while the background component in shown in red (dotted).

Figure 2

Combined invariant-mass distribution $m(K_{\mathrm{S}}^0{K}_{\mathrm{S}}^0)$ of the signal decay channel. The black (solid) curve represents the complete model, the $B_s^0$ signal component is given in green (dashed), the smaller $B^0$ signal is given in blue (dash-dotted) and the background component in red (dotted).

Figure 3

Fits to the invariant-mass distribution $m(K_{\mathrm{S}}^0{K}^{+}{K}^{-})$ of the normalization decay channel. The black curve represents the complete model, the $B^0\to \varphi K_{\mathrm{S}}^0$ component is given in green (dashed), while the background component in shown in red (dotted).

Figure 4

Fits to the invariant-mass distribution $m(K^{+}{K}^{-})$ of $B^0\to \varphi K_{\mathrm{S}}^0$ data weighted using the ${}_s\mathcal{P}\mathrm{lot}$ technique. The blue curve represents the complete model, the signal $\varphi$ component is given in green (dashed), and the background $f_0(980)\to K^{+}{K}^{-}$ model is shown in black (dotted).