Measurement of the Bs to mu mu branching fraction and search for B0 to mu mu with the CMS Experiment

Results are presented from a search for the rare decays Bs to mu mu and B0 to mu mu in pp collisions at sqrt(s)=7 and 8 TeV, with data samples corresponding to integrated luminosities of 5 and 20 inverse femtobarns, respectively, collected by the CMS experiment at the LHC. An unbinned maximum-likelihood fit to the dimuon invariant mass distribution gives a branching fraction B(Bs to mu mu) = (3 +1.0/-0.9)E-9, where the uncertainty includes both statistical and systematic contributions. An excess of Bs to mu mu events with respect to background is observed with a significance of 4.3 standard deviations. For the decay B0 to mu mu an upper limit of B(B0 to mu mu) < 1.1E-9 at the 95% confidence level is determined. Both results are in agreement with the expectations from the standard model.