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

V. Khachatryan, A.M. Sirunyan, A. Tumasyan, W. Adam, T. Bergauer, M. Dragicevic, J. Erö, M. Friedl, R. Frühwirth, V.M. Ghete, C. Hartl, N. Hörmann (+2135 others)
2015 Physics Letters B  
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 to mu tau[e] and H to mu tau[h] channels, where tau[e] and tau[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 sqrt(s) = 8 TeV with the CMS experiment at the CERN LHC and corresponds to an integrated
more » ... ity of 19.7 inverse femtobarns. 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 to mu tau) = (0.84 +0.39 -0.37)%. A constraint on the branching fraction, B(H to mu tau) < 1.51% at 95% confidence level is set. This limit is subsequently used to constrain the mu-tau Yukawa couplings to be less than 3.6E-3.
doi:10.1016/j.physletb.2015.07.053 fatcat:rhy2xa5wjfhhnac5libti6vof4