Results on B_S⁰ →μ⁺μ^- decays with the CMS experiment

Results are reported on B_S⁰ →μ⁺μ^- decays using 61 fb^-1 of proton-proton collision data obtained in 2011-2016 with the CMS experiment at the LHC (CERN). In the standard model (SM) of particle physics this decay can be precisely calculated with small theoretical uncertainties, making it an excellent probe for testing the limits of the SM. The branching fraction BF(B_S⁰ →μ⁺μ^-)=(2.9 ± 0.7) x 10^-9 is measured with a statistical significance of 5.6 standard deviations. In addition, the effective lifetime of this decay is measured as 𝜏_𝜇𝜇=1.70+0.61−0.44

ps. Both results are in good agreement with the SM prediction. In comparison to the previous analysis, a much improved muon identification algorithm significantly increased the purity and strongly reduced the background. As a consequence, the measurement of BF(B⁰ →μ⁺μ^-) < 3.6 x 10^-10 at 95% CL is no longer in tension to the SM, but fully compatible with it.