Searches for lepton-flavour-violating decays of the Higgs boson in $\sqrt{s}=13$ TeV $pp$ collisions with the ATLAS detector

Abstract

This Letter presents direct searches for lepton flavour violation in Higgs boson decays, $H\to e\tau$ and $H\to \mu \tau$, performed with the ATLAS detector at the LHC. The searches are based on a data sample of proton-proton collisions at a centre-of-mass energy $\sqrt{s}=13$ TeV, corresponding to an integrated luminosity of $36.1{\mathrm{fb}}^{-1}$. No significant excess is observed above the expected background from Standard Model processes. The observed (median expected) 95 % confidence-level upper limits on the lepton-flavour-violating branching ratios are $0.47\%$ ($0.34_{-0.10}^{+0.13}\%$) and $0.28\%$ ($0.37_{-0.10}^{+0.14}\%$) for $H\to e\tau$ and $H\to \mu \tau$, respectively.

39 pages in total, author list starting page 23, 5 figures, 6 tables. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HIGG-2017-08

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