Abstract
A search for the decay $K^0_S \to \mu^+\mu^-$ is performed, based on a data sample of proton-proton collisions corresponding to an integrated luminosity of $3 fb^{−1}$, collected by the LHCb experiment at centre-of-mass energies of 7 and 8TeV. The observed yield is consistent with the background-only hypothesis, yielding a limit on the branching fraction of $\mathcal{B}(K^0_S \to \mu^+\mu^−) < 0.8 (1.0) × 10^{−9}$ at 90% (95%) confidence level. This result improves the previous upper limit on the branching fraction by an order of magnitude.
LHCb Collaboration