Study of DiMuon Rare Beauty Decays with ATLAS and CMS

The LHC experiments will perform sensitive tests of physics beyond the Standard Model (BSM). Investigation of decays of beauty hadrons represents an alternative approach in addition to direct BSM searches. The ATLAS and CMS efforts concentrate on those B-decays that can be easily selected already at the first and second level trigger. The most favorable trigger signature will be for $B$-hadron decays with muons in the final state. Using this trigger, ATLAS and CMS will be able to accommodate unprecedentedly high statistics in the rare decay sector. These are purely dimuon decays, and families of semimuonic exclusive channels. Already with \ensuremath{1fb^{-1}} the sensitivity in the dimuon channels will be comparable to today world statistics. The strategy is to carry on the dimuon channel program up to nominal LHC luminosity. In particular the \ensuremath{B_s \to \mu\mu} signal with \ensuremath{\sim}5 sigma significance can be measured combining low luminosity \ensuremath{10^{33}cm^{-2} s^{-1}} samples with those of one year of LHC operation at a luminosity of \ensuremath{10^{34}cm^{-2} s^{-1}}. This precision will allow to exclude or to confirm the SM unambiguously.