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

Abstract

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<inf>e</inf> and H→μτ<inf>h</inf> channels, where τ<inf>e</inf> and τ<inf>h</inf> 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<inf>H</inf>=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.