Observation of the Higgs boson decay to a pair of τ leptons with the CMS detector

A measurement of the H → τ τ signal strength is performed using events recorded in proton–proton collisions by the CMS experiment at the LHC in 2016 at a center-of-mass energy of 13 TeV . The data set corresponds to an integrated luminosity of 35.9 fb − 1 . The H → τ τ signal is established with a significance of 4.9 standard deviations, to be compared to an expected significance of 4.7 standard deviations. The best fit of the product of the observed H → τ τ signal production cross section and branching fraction is 1.09 − 0.26 + 0.27 times the standard model expectation. The combination with the corresponding measurement performed with data collected by the CMS experiment at center-of-mass energies of 7 and 8 TeV leads to an observed significance of 5.9 standard deviations, equal to the expected significance. This is the first observation of Higgs boson decays to τ leptons by a single experiment.