Search for the rare decay KS^0to {μ+}{μ-}

A search for the decay K_S^0to {μ⁺}{μ^-} is performed, based on a data sample of 1.0 fb^-1 of pp collisions at sqrt{s}=7TeV collected by the LHCb experiment at the Large Hadron Collider. The observed number of candidates is consistent with the background-only hypothesis, yielding an upper limit of {B}( {K_S^0to {μ⁺}{μ^-}} ) < 11(9) × 10^-9 at 95 (90)% confidence level. This limit is a factor of thirty below the previous measurement.