CMS measurements of rare B meson decays to two muons

We report a measurement of the B 0s → µ + µ − branching fraction and its effective lifetime, as well as results of a search for the B 0 → µ + µ − decay in proton-proton collisions at √ s = 13 TeV at the LHC. The analysis is based on data collected with the CMS detector in 2016-2018 corresponding to an integrated luminosity of 140 fb − 1 . The measured branching fraction of the B 0s → µ + µ − decay and the effective B 0s lifetime are the most precise measurements to date. No evidence for the B 0 → µ + µ − decay has been found. All results are found to be consistent with the standard model predictions.