Measurement of properties of B(s)(0) -> mu(+)mu(-) decays and search for B0 -> mu(+)mu(-) 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 7TeV (5 fb-1), 8TeV (20 fb-1), and 13TeV (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 B0 → 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.