Search for the rare decay $K_S^0 \to \mu^+ \mu^-$

A search for the decay $K_S^0 \to \mu^+ \mu^-$ 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 $B(K_S^0 \to \mu^+ \mu^-) < 11(9) × 10^{−9}$ at 95 (90)% confidence level. This limit is a factor of thirty below the previous measurement.