# Measurement of the branching fraction of the decay $B_s^0\to K_S^0 K_S^0$

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## Abstract

A measurement of the branching fraction of the decay $B_s^0 \to K_S^0 K_S^0$ is performed using proton-proton collision data corresponding to an integrated luminosity of 5 $fb^{-1}$ collected by the LHCb experiment between 2011 and 2016. The branching fraction is determined to be BR($B_s^0 \to K_S^0 K_S^0$) = [8.3 $\pm$ 1.6 (stat) $\pm$ 0.9 (syst) $\pm$ 0.8 (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 $B^0 \to \phi K_S^0$ 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 $B^0 \to K_S^0 K_S^0$ is performed relative to that of the $B_s^0 \to K_S^0 K_S^0$ channel, and is found to be $\frac{BR(B^0 \to K_S^0 K_S^0)}{BR(B_s^0 \to K_S^0 K_S^0)}$ = [7.5 $\pm$ 3.1 (stat) $\pm$ 0.5 (syst) $\pm$ 0.3 ($f_s/f_d$)] $\times 10^{-2}$.

## Figures and captions

 Fits to the invariant-mass distribution $m( K ^0_{\mathrm{S}} K ^+ K ^- )$ of the normalization decay channel. The black curve represents the complete model, the $B ^0 \rightarrow \phi K ^0_{\mathrm{S}}$ component is given in green (dashed), while the background component in shown in red (dotted). B2phiK[..].pdf [19 KiB] HiDef png [223 KiB] Thumbnail [180 KiB] *.C file B2phiK[..].pdf [19 KiB] HiDef png [216 KiB] Thumbnail [178 KiB] *.C file Combined invariant-mass distribution $m( K ^0_{\mathrm{S}} K ^0_{\mathrm{S}} )$ of the signal decay channel. The black (solid) curve represents the complete model, the $B ^0_ s$ 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). B2KSKS[..].pdf [17 KiB] HiDef png [200 KiB] Thumbnail [162 KiB] *.C file Fits to the invariant-mass distribution $m( K ^0_{\mathrm{S}} K ^+ K ^- )$ of the normalization decay channel. The black curve represents the complete model, the $B ^0 \rightarrow \phi K ^0_{\mathrm{S}}$ component is given in green (dashed), while the background component in shown in red (dotted). B2phiK[..].pdf [18 KiB] HiDef png [223 KiB] Thumbnail [175 KiB] *.C file B2phiK[..].pdf [18 KiB] HiDef png [222 KiB] Thumbnail [179 KiB] *.C file Fits to the invariant-mass distribution $m( K ^+ K ^- )$ of $B ^0 \rightarrow \phi K ^0_{\mathrm{S}}$ data weighted using the ${}_s\mathcal{P}\text{lot}$ technique. The blue curve represents the complete model, the signal $\phi$ component is given in green (dashed), and the background $f_0(980) \rightarrow K ^+ K ^-$ model is shown in black (dotted). B2phiK[..].pdf [16 KiB] HiDef png [210 KiB] Thumbnail [174 KiB] *.C file B2phiK[..].pdf [16 KiB] HiDef png [214 KiB] Thumbnail [182 KiB] *.C file B2phiK[..].pdf [16 KiB] HiDef png [211 KiB] Thumbnail [173 KiB] *.C file B2phiK[..].pdf [16 KiB] HiDef png [216 KiB] Thumbnail [176 KiB] *.C file Animated gif made out of all figures. PAPER-2019-030.gif Thumbnail

## Tables and captions

 Results of the simultaneous fit to the invariant mass of the $K ^0_{\mathrm{S}} K ^0_{\mathrm{S}}$ system. The fit results for $\mathcal{B}$ and $f_{ B ^0 / B ^0_ s }$ are shared among all data categories. The given uncertainties are statistical only. The normalization constant $\alpha$ and the corresponding normalization channel yields $N_{\text{norm}}$ are shown for reference. Table_1.pdf [85 KiB] HiDef png [66 KiB] Thumbnail [30 KiB] tex code All systematic uncertainties on the $B ^0_ s \rightarrow K ^0_{\mathrm{S}} K ^0_{\mathrm{S}}$ branching fraction, presented as relative measurements. The last row shows the combined systematic uncertainty for each data sample. Table_2.pdf [50 KiB] HiDef png [91 KiB] Thumbnail [38 KiB] tex code

Created on 06 March 2021.