A search for the decay $K^0_{ \mathrm{ S}}\rightarrow\mu^{ +}\mu^{ -}$ 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 ${ \cal B}(K^0_{ \mathrm{ S}}\rightarrow\mu^{ +}\mu^{ -}) < 2.2 \times 10^{ -10}$ at 90% CL. The limit reduces to ${ \cal B}(K^0_{ \mathrm{ S}}\rightarrow\mu^{ +}\mu^{ -}) < 2.1 \times 10^{ -10}$ at 90% CL once combined with the result from data taken in 2011 and 2012.
Categories: hep-ex