Constraints on the $K_{\mathrm{S}}^0\to {\mu }^{+}{\mu }^{-}$ branching fraction

Abstract

A search for the decay $K_{\mathrm{S}}^0\to {\mu }^{+}{\mu }^{-}$ is performed using proton-proton collision data, corresponding to an integrated luminosity of $5.6{\text{fb}}^{-1}$ and collected with the LHCb experiment during 2016, 2017 and 2018 at a center-of-mass energy of $13\mathrm{TeV}$. The observed signal yield is consistent with zero, yielding an upper limit of $\mathcal{B}(K_{\mathrm{S}}^0\to {\mu }^{+}{\mu }^{-})<2.2\times 10^{-10}$ at 90% CL. The limit reduces to $\mathcal{B}(K_{\mathrm{S}}^0\to {\mu }^{+}{\mu }^{-})<2.1\times 10^{-10}$ at 90% CL once combined with the result from data taken in 2011 and 2012.

All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2019-038.html