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

## TL;DR

This paper reports on searches for lepton-flavour-violating decays of the Higgs boson into eτ and μτ final states using 13 TeV proton-proton collision data from the ATLAS detector, setting upper limits on these rare decay modes.

## Contribution

First direct search for H→eτ and H→μτ decays at 13 TeV with ATLAS, establishing new upper limits on their branching ratios.

## Key findings

- No significant excess observed above background.
- Upper limits on branching ratios are 0.47% for H→eτ and 0.28% for H→μτ.
- Results constrain models predicting lepton-flavour violation in Higgs decays.

## Abstract

This Letter presents direct searches for lepton flavour violation in Higgs boson decays, $H\rightarrow e\tau$ and $H\rightarrow\mu\tau$, 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 $0.47\%$ ($0.34^{+0.13}_{-0.10}\,\%$) and $0.28\%$ ($0.37^{+0.14}_{-0.10}\,\%$) for $H\to e\tau$ and $H\to\mu\tau$, respectively.