Study of the performance of the muon and tau identification at ATLAS

Charged leptons play an important role in the physics programme at the LHC. The performance of identification of charged leptons must be know with high precision. This talk present the studies of the muon and tau identification performance at the ATLAS experiment. In 2012 the LHC is operated in a mode leading to up to 40 inelastic pp collisions per bunch crossing, so-called ”pile-up”, with an average number of 20 inelastic collisions. The high multiplicity of charged tracks in the inner tracking detector makes it difficult to reconstruct and identify muons at high efficiency and low misidentification rate. Di-muon decays of J/ψ mesons and Z bosons have been used to study the muon reconstruction and identification efficiency as a function of the muon transverse momentum from pT = 4 GeV to pT = 100 GeV and the number of inelastic collisions per event. The misidentification rate was determined with Z+jet events. 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 by W->taunu and Z->tautau events. The energy scale uncertainties for tau leptons are determined by investigating single hadron calorimeter response, as well as kinematic distributions in Z->tautau events.