Probing lepton flavour violation via neutrinoless τ −→ 3 μ decays with the ATLAS detector

This article presents the sensitivity of the ATLAS experiment to the lepton-flavour-violating decays of τ → 3 μ . A method utilising the production of τ leptons via W → τν decays is used. This method is applied to the sample of 20.3 fb − 1 of pp collision data at a centre-of-mass energy of 8 TeV collected by the ATLAS experiment at the LHC in 2012. No event is observed passing the selection criteria, and the observed (expected) upper limit on the τ lepton branching fraction into three muons, Br (τ → 3 μ) , is 3 . 76 × 10 − 7 (3 . 94 × 10 − 7 ) at 90 % confidence level.

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