Measurement of the Mis-identification Probability of τ Leptons from Hadronic Jets and from Electrons

Measurements of the mis-identification probability of QCD jets and electrons as hadronically decaying τ leptons using tag-and-probe methods are described. The analyses are based on 35pb−1 of proton-proton collision data, taken by the ATLAS experiment at a center-of-mass energy of sqrt(s) = 7 TeV. The mis-identification probabilities range between 10% and 0.1% for QCD jets, and about (1 − 2)% for electrons. They depend on the identification algorithm chosen, the pT and the number of prongs of the τ candidate, and on the amount of pile up present in the event.