Search for Tau $\rightarrow$ 3mu decays with CMS experiment at LHC

The search for the charged lepton flavor violating decay $\tau \rightarrow 3\mu$ has been performed at the CMS experiment at the LHC, using data collected in 2016 during proton-proton collisions. The data sample corresponds to an integrated luminosity of 33.2 fb$^{-1}$, recorded at a center-of-mass energy of 13 TeV. The results obtained by exploiting tau leptons produced in decays of heavy flavor B and D mesons and from W bosons have been combined and they are presented in this contribution. No significant excess was observed and an upper limit on the branching fraction of B($\tau \rightarrow 3\mu$) of 8.0 x 10$^{-8}$ at 90\% confidence level was set.