Measurement of properties of B0s→ μ+μ− decays and search for B0→ μ+μ− with the CMS experiment

Results are reported for the B0s → µ+µ − branching fraction and effective lifetime and from a search for the decay B0 → µ+µ−. The analysis uses a data sample of proton-proton collisions accumulated by the CMS experiment in 2011, 2012, and 2016, with center-of-mass energies (integrated luminosities) of 7 TeV (5 fb−1), 8 TeV (20 fb−1), and 13 TeV (36 fb−1). The branching fractions are determined by measuring event yields relative to B+ → J/ψK+ decays (with J/ψ → µ+µ-, which results in the reduction of many of the systematic uncertainties. The decay B0s → µ+µ− is observed with a significance of 5.6 standard deviations. The branching fraction is measured to be B(B0s → µ+µ−) = [2.9 ± 0.7(exp) ± 0.2(frag)] × 10−9, where the first uncertainty combines the experimental statistical and systematic contributions, and the second is due to the uncertainty in the ratio of the B0s and the B+ fragmentation functions. No significant excess is observed for the decay B0 → µ+µ−, and an upper limit of B(B0 → µ+µ−) < 3.6×10−10 is obtained at 95% confidence level. The B0s → µ+µ− effective lifetime is measured to be τ µ+µ− = 1.70 +0.61−0.44 ps. These results are consistent with standard model predictions.