Limit on $B_s^0 \to \mu+\mu^-$ branching fraction based on $4.9~\mathrm{fb}^{-1}$ of integrated luminosity

This note documents the ATLAS analysis searching for $B_s^0 \to \mu^+\mu^-$ decays with an integrated luminosity of 4.9 fb$^{-1}$, corresponding to the full 2011 proton-proton dataset. This analysis supersedes the previous result based on 2.4 fb$^{-1}$. We derive a limit on ${\cal B}(B_s^0 \to \mu^+ \mu^-) <1.5\;(1.2) \times 10^{-8}$ at 95% (90%) CL.