LHCb potential to measure/exclure the branching ratio of the decay $Bs \to \mu^{+}\mu^{-}$

This note describes the potential of LHCb to reach sensitivities of the order of 10-9 in the decay of Bs -> mu+ mu-. The large background expected in the search for this decay is kept under control due to the excellent tracking performance of LHCb (namely the invariant mass resolution ~18 MeV/c2), and the good muon-identification capabilities. The LHCb trigger selects these events efficiently. LHCb has the potential to exclude the interesting region between 10-8 and the SM prediction with very little luminosity (~0.5 fb-1), and has the potential to claim a 3 sigma (5 sigma) observation (discovery) of the SM prediction with ~2 fb-1 (~6 fb-1) of data.