Search for Lepton-Flavor-Violating Decays of the Higgs Boson

The first direct search for lepton-flavor-violating decays of the recently discovered Higgs boson is described. The search is performed in the $H \rightarrow \mu\tau_{e}$ and $H \rightarrow \mu\tau_{h}$ channels where $\tau_{e}$ and $\tau_{h}$ are taus 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 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. Interpreted as a limit this results in a constraint on the branching fraction, $B(H \rightarrow \mu\tau) < 1.51\%$ at 95$\%$ confidence level. The best fit branching fraction is $B(H \rightarrow \mu\tau) = (0.84^{+0.39}_{-0.37})\%$. The limit is subsequently used to constrain the $Y_{\mu\tau}$ Yukawa coupling, $\sqrt{|{Y_{\mu\tau}|}^2 + {|Y_{\tau\mu}|}^2} < 3.6 \times 10^{-3}$.