UC Santa Cruz

This article presents the sensitivity of the ATLAS experiment to the lepton-flavour-violating decays of τ→3μ$$\tau \rightarrow 3\mu $$. A method utilising the production of τ$$\tau $$ leptons via W→τν$$W\rightarrow \tau u $$ decays is used. This method is applied to the sample of 20.3 fb-1$$^{-1}$$ 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$$\tau $$ lepton branching fraction into three muons, Br(τ→3μ)$$\mathrm{Br}(\tau \rightarrow 3\mu )$$, is 3.76×10-7$$3.76\times 10^{-7}$$ (3.94×10-7$$3.94\times 10^{-7}$$) at 90 % confidence level.