Search for lepton-flavour-violating decays of the Higgs and $Z$ bosons with the ATLAS detector

Direct searches for lepton flavour violation in decays of the Higgs and Z bosons with the ATLAS detector at the LHC are presented. The following three decays are considered: $H\rightarrow e\tau $ , $H\rightarrow \mu \tau $ , and $Z\rightarrow \mu \tau $ . The searches are based on the data sample of proton–proton collisions collected by the ATLAS detector corresponding to an integrated luminosity of 20.3 $\mathrm{fb}^{-1}$ at a centre-of-mass energy of $\sqrt{s}=8$ TeV. No significant excess is observed, and upper limits on the lepton-flavour-violating branching ratios are set at the 95 $\%$ confidence level: Br $(H\rightarrow e\tau )<1.04\%$ , Br $(H\rightarrow \mu \tau )<1.43\%$ , and Br $(Z\rightarrow \mu \tau )<1.69\times 10^{-5}$ .