UC Santa Cruz

This paper presents a measurement of the polarisation of τ$$\tau $$ leptons produced in Z/γ∗→ττ$$Z/\gamma ^{*}\rightarrow \tau \tau $$ decays which is performed with a dataset of proton—proton collisions at s=8$$\sqrt{s}=8$$ TeV, corresponding to an integrated luminosity of 20.2 fb-1$$^{-1}$$ recorded with the ATLAS detector at the LHC in 2012. The Z/γ∗→ττ$$Z/\gamma ^{*}\rightarrow \tau \tau $$ decays are reconstructed from a hadronically decaying τ$$\tau $$ lepton with a single charged particle in the final state, accompanied by a τ$$\tau $$ lepton that decays leptonically. The τ$$\tau $$ polarisation is inferred from the relative fraction of energy carried by charged and neutral hadrons in the hadronic τ$$\tau $$ decays. The polarisation is measured in a fiducial region that corresponds to the kinematic region accessible to this analysis. The τ$$\tau $$ polarisation extracted over the full phase space within the Z/γ∗$$Z/\gamma ^{*}$$ mass range of 66