## Abstract

The charmless three-body decays $B^0_{(s)} \to K_s^0 h^+ h^{\prime-}$ (where $h^{(\prime)} = \pi, K$) are analysed using a sample of $pp$ collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 3 fb$^{−1}$. The branching fractions are measured relative to that of the $B^0 \to K_S^0\pi^+\pi^-$ decay, and are determined to be:

$\frac{\mathcal{B}(B^0 \to K_S^0K^{\pm}\pi^{\mp})}{\mathcal{B}(B^0 \to K_S^0K^+\pi^-)} = 0.123 \pm 0.009(stat) \pm 0.015(syst)$,

$\frac{\mathcal{B}(B^0 \to K_S^0K^+K^-)}{\mathcal{B}(B^0 \to K_S^0\pi^+\pi^-)} = 0.549 \pm 0.018(stat) \pm 0.033(syst)$,

$\frac{\mathcal{B}(B_S^0 \to K_S^0\pi^+\pi^-)}{\mathcal{B}(B^0 \to K_S^0\pi^+\pi^-)} = 0.191 \pm 0.027(stat) \pm 0.031(syst) \pm 0.011(f_s/f_d)$,

$\frac{\mathcal{B}(B_S^0 \to K_S^0K^{\pm}\pi^{\mp})}{\mathcal{B}(B^0 \to K_S^0\pi^+\pi^-)} = 1.70 \pm 0.07(stat) \pm 0.11(syst) \pm 0.10(f_s/f_d)$,

$\frac{\mathcal{B}(B_S^0 \to K_S^0K^+K^-)}{\mathcal{B}(B^0 \to K_S^0\pi^+\pi^-)} \in [0.008−0.051]$ at 90% confidence level,

where $f_s/f_d$ represents the ratio of hadronisation fractions of the $B_s^0$ and $B^0$ mesons.