Updated limit for the decay $K_{\rm\scriptscriptstyle S}^0\rightarrow\mu^+\mu^-$

A search is performed for the decay $K_{\rm\scriptscriptstyle S}^0\rightarrow\mu^+\mu^-$, using the data sample of $pp$ collisions at $\sqrt{s}=8$ TeV collected by the LHCb experiment at the Large Hadron Collider in 2012, corresponding to an integrated luminosity of 2.0 fb$^{-1}$. In the Standard Model, the decay is expected to be suppressed at a level below the experimental sensitivity, but could be enhanced by new sources of $CP$ violation. The observed number of candidates is compatible with the expected background and allows to set an upper limit $\mathcal{B}(K_{\rm\scriptscriptstyle S}^0\rightarrow\mu^{+}\mu^{-}) < 6.9 (5.8)\times10^{-9}$ at $95~ (90)\%$ confidence level. This limit improves the result published by LHCb using 1.0 fb$^{-1}$ of collisions collected in 2011 at $\sqrt{s}=7$ TeV.