Measurement of properties of Bₛ⁰ → μ+μ− decays and search for B0 → μ+μ− with the CMS experiment

A bstract Results are reported for the Bₛ⁰ B s 0 → μ + μ − branching fraction and effective lifetime and from a search for the decay B 0 → 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 Bₛ⁰ B s 0 → μ + μ − is observed with a significance of 5.6 standard deviations. The branching fraction is measured to be B(Bₛ⁰→ ⁺⁻)=[2.9± 0.7(exp )± 0.2(frag)]× 10⁻⁹ ℬ B s 0 → 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 Bₛ⁰ B s 0 and the B + fragmentation functions. No significant excess is observed for the decay B 0 → μ + μ − , and an upper limit of ℬ(B 0 → μ + μ − ) < 3.6 × 10 −10 is obtained at 95% confidence level. The Bₛ⁰ B s 0 → μ+μ − effective lifetime is measured to be τ_⁺⁻=1.70-0.44+0.61 τ μ + μ − = 1.70 − 0.44 + 0.61 ps. These results are consistent with standard model predictions.