We report the first search for the penguin-dominated process $B_s^0\to {\eta }^{\prime }{X}_{s\overline{s}}$ using a semi-inclusive method. A $121.4{\mathrm{fb}}^{-1}$ integrated luminosity $\mathrm{\Upsilon }(5S)$ data set collected by the Belle experiment, at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider, is used. We observe no statistically significant signal and, including all uncertainties, we set a 90% confidence level upper limit on the partial branching fraction at $1.4\times {10}^{-3}$ for $M(X_{s\overline{s}})\le 2.4\mathrm{GeV}/c^2$.

• Received 19 February 2021
• Accepted 4 June 2021

DOI:https://doi.org/10.1103/PhysRevD.104.012007

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Published by the American Physical Society