CMS collaboration (2225 authors)Hollar, JonathanNayak, ArunaCalpas, BettyAlmeida, NunoBargassa, PedrameBeirão Da Cruz E Silva, CristóvãoFaccioli, PietroFerreira Parracho, Pedro GuilhermeGallinaro, MicheleNguyen, FedericoRodrigues Antunes, JoaoSeixas, JoaoVarela, JoaoVischia, PietroLloret Iglesias, LaraDavid Tinoco Mendes, AndreMusella, PasqualeSilva, PedroPela, JoaoLeonardo, Nuno2019-02-032019-02-032013-09-05http://dx.doi.org/10.1103/PhysRevLett.111.101804http://hdl.handle.net/10400.26/26450Results are presented from a search for the rare decays B(s) 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(B(s) to mu+ mu-) = (3 +1.0/-0.9)E-9, where the uncertainty includes both statistical and systematic contributions. An excess of B(s) 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.engjournal article2019-02-03