  A search for the rare decays B_s to mu+ mu- and B^0 to mu^+ mu^- is performed
in pp collisions at sqrt(s) = 7 TeV, with a data sample corresponding to an
integrated luminosity of 5 inverse femtobarns collected by the CMS experiment
at the LHC. In both decays, the number of events observed after all selection
requirements is consistent with the expectation from background plus standard
model signal predictions. The resulting upper limits on the branching fractions
are Br(B_s to mu^+ mu^-) < 7.7E-9 and Br(B^0 to mu^+ mu^-) < 1.8E-9 at 95%
confidence level.
