# Dortmund 2021 – wissenschaftliches Programm

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# T: Fachverband Teilchenphysik

## T 5: Higgs decay in fermions I

### T 5.7: Vortrag

### Montag, 15. März 2021, 17:30–17:45, Te

Search for lepton-flavour violating decays of the Higgs boson using the symmetry method for background estimation with the ATLAS experiment at √s=13 TeV — •Katharina Schleicher, Valerie Lang, and Markus Schumacher — University of Freiburg

The discovery of the Higgs boson opened the window to a variety of interesting probes to physics beyond the standard model (SM), including searches for lepton-flavour violating (LFV) Higgs-boson decays. These are predicted in several models, including supersymmetric extensions of the SM and general two-higgs-dublet models. In nature, LFV was already observed in form of neutrino oscillations. In this analysis the decays of H→ eτ and H→µτ with leptonic τ-decays leading to eµ+2ν final states are considered. A central part of the analysis is the precise estimation of the SM backgrounds. Therefore, a data-driven method is used - the so-called symmetry method. It exploits two principles: First, SM backgrounds with prompt leptons are symmetric w.r.t. electrons and muons. And second, this symmetry is broken if the branching ratios of the two LFV decays are of different magnitude. The first principle implicates the challenge of restoring this symmetry since electrons and muons are experimentally different. The second principle is motivated by the upper limit on µ → eγ. To obtain the best possible sensitivity, a dedicated statistical model was developed and neural networks for classification are deployed. In this talk, an overview of the analysis using the LHC Run-2 dataset recorded with the ATLAS detector in p-p collisions at √s=13 TeV is given.