Abstract:
Measurements are presented of the B0s & RARR; & mu;+& mu;- branching fraction and effective lifetime, as well as results of a search for the B0 & RARR; & mu;+& mu;- decay in proton-proton collisions at & RADIC;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 branching fraction of the B0s & RARR; & mu;+& mu;- decay and the effective B0s meson lifetime are the most precise single measurements to date. No evidence for the B0 & RARR; & mu;+& mu;- decay has been found. All results are found to be consistent with the standard model predictions and previous measurements.