Searches for lepton-flavour violating decays of the Higgs boson into eτ and μτ in √(s) = 13 TeV pp collisions with the ATLAS detector

Abstract

Direct searches for lepton-flavour-violating decays of the Higgs boson into eτ and μτ final states with the ATLAS detector at the LHC with Run-2 data are presented. Both leptonically and hadronically decaying τ-leptons are included and two different background estimation techniques are employed: a MC-template method, based on data-corrected simulation samples, and a data-driven method, based on exploiting the symmetry between electrons and muons in the Standard Model backgrounds. Observed (Expected) upper limits are set on the branching ratios at 95 % confidence level, ℬ(H → eτ)<0.20 % (0.12 %) and ℬ(H → μτ)<0.18% (0.09 %), and a best-fit branching ratio difference, ℬ(H → μτ) - ℬ(H → eτ), of 0.25 ± 0.10 % is found in the channel where the τ-lepton decays to leptons, compatible with a value of zero within 2.5 σ.