The study of extremely rare or forbidden processes allows the indirect search for new physics through the comparison with the standard model expectations. The leptonic decays of B0s and B0 mesons are flavor changing neutral currents
processes highly suppressed in the standard model, with small predicted branching fractions. A search for the rare decays B0s (B0) → μ+μ− is performed in pp collisions at √s = 7TeV, with a data sample corresponding to an integrated luminosity of 5 fb−1 collected by the CMS experiment at the LHC. The number of observed events is consistent with the background plus standard model signal expectation. The resulting upper limits on the branching fractions are B(B0s
→ μ+μ−) < 7.7 × 10−9 and B(B0 → μ+μ−) < 1.8 × 10−9 at 95% confidence level
