Measurement of ${\rm B^0_s}\to\mu^+\mu^-$ decay properties and search for the ${\rm B}^0\to\mu\mu$ decay in proton-proton collisions at $\sqrt{s}=13~\rm{TeV}$

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