Search for lepton-flavour-violating decays of the Higgs boson

The first direct search for lepton-flavour-violating decays of the recently discovered Higgs boson (H) is described. The search is performed in the H→μτ_e and H→μτ_h channels, where τ_e and τ_h are tau leptons reconstructed in the electronic and hadronic decay channels, respectively. The data sample used in this search was collected in pp collisions at a centre-of-mass energy of s=8 TeV with the CMS experiment at the CERN LHC and corresponds to an integrated luminosity of 19.7 fb⁻¹. The sensitivity of the search is an order of magnitude better than the existing indirect limits. A slight excess of signal events with a significance of 2.4 standard deviations is observed. The p-value of this excess at M_H=125 GeV is 0.010. The best fit branching fraction is B(H→μτ)=(0.84_−0.37 ^+0.39)%. A constraint on the branching fraction, B(H→μτ)<1.51% at 95% confidence level is set. This limit is subsequently used to constrain the μ–τ Yukawa couplings to be less than 3.6×10⁻³.