Performance of muon and tau identification at ATLAS

Charged leptons play an important role in the physics programme at the Large Hadron Collider. The performance of identification of charged leptons , therefore, must be known with high precision. In 2012 the LHC is operated in a mode leading to upto 40 inelastic pp collisions per bunch crossing, so-called ``pile-up'', with an average number of 20 inelastic collisions. This contribution presents the studies of the muon and tau identification performance at the ATLAS experiment. Di-muon decays of $J/psi$ mesons and Z bosons have been used to study the muon reconstruction and identification efficiency as a function of the muon transverse momentum and the number of inelastic collisions per event. Optimal identification of hadronically decaying tau leptons is achieved by using detailed information from tracking and calorimeter detector components. Variables describing the properties of calorimeter energy deposits and track reconstruction within tau candidates are combined in multi-variate discriminants, to achieve high rejection against backgrounds, which is challenging in high luminosity environments. The identification efficiencies are measured using $W ightarrow au u$ and $Z ightarrow au au$ events. The energy scale uncertainties for tau leptons are determined by investigating single hadron calorimeter response, as well as kinematic distributions in $Z ightarrow au au$ events.