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

This article presents the sensitivity of the ATLAS experiment to the lepton-flavour-violating decays of τ→3μ . 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→3μ) , is 3.76×10-7 ( 3.94×10-7 ) at 90 % confidence level.