Measurement of the e $B^0_s$ → μ+μ− decay properties and search for the B0 → μ+μ− decay in proton-proton collisions at √s = 13 TeV

Measurements are presented of the $B^0_s \rightarrow \mu \mu$ branching fraction and effective lifetime, as well as results of a search for the $B^0 \rightarrow \mu \mu$ decay in proton-proton collisions at $\sqrt(s)$ = 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 $B^0_s \rightarrow \mu \mu$ decay and the effective B0s meson lifetime are the most precise single measurements to date. No evidence for the $B^0 \rightarrow \mu \mu$ decay has been found. All results are found to be consistent with the standard model predictions and previous measurements.