CERN-THESIS-2012-153 26/07/2012 - CERN Document Server

5.2 Trigger
This analysis requires collision data selected by inclusive single electron and muon triggers, with pT thresholds
of 18 GeV for muons and 20 or 22 GeV for electrons, depending on the data taking period. Specifically, the
lowest unprescaled trigger chains are used. To ensure that the event is triggered by the lepton candidates
selected by the analysis (see Section 5.3), one of the leptons and the trigger object are required to match
within ∆R < 0.15.
5.3 Object Definition
After the offline reconstruction, additional requirements are applied to the reconstructed objects. Moreover,
to increase the acceptance of the analysis, leptons are also selected based purely on the inner detector track
information. Thus, leptons are selected either using the full ATLAS detector, including the inner detector,
calorimeter and muons spectrometer (‘identified leptons’ or ‘ID leptons’), or using only a high quality inner
detector track (‘track leptons’ or ‘TLs’). These TLs recover areas of inefficiency in the standard lepton
identification algorithms and also have sensitivity to hadronic tau decays.
5.3.1 Muons
Muons are detected and measured in the muon spectrometer, which is instrumented with separate trigger
and high-precision tracking chambers. Muon momentum is measured via the curvature of the trajectory in
the toroidal magnetic field on the spectrometer and the solenoidal field of the inner detector. In the case
of muon, tracks from both the muon spectrometer and the inner detector are matched to give combined
tracks. Only muons passing tight track quality requirements are considered. Muon candidates are required
to have a transverse momenta larger than 20 GeV. Due to the geometrical constraints of the inner detector
fiducial region, muons must have |η| < 2.5. Both calorimeter- and track-based isolation requirements are
applied to the muons, to select candidates consistent with originating from W- and Z-bosons decay. The
track-based isolation, defined as the sum of transverse momenta of tracks with pT > 1 GeV, inside a cone of
size ∆R = 0.3 around the muon, must be less than 4 GeV. Similarly, the energy deposited in the calorime-
ter inside a cone of size ∆R = 0.3 around the muon (ignoring the energy of the muon), i.e. calorimeter
isolation, must be less than 4 GeV. Additionally, to further reject muons from heavy flavor decays, muon
candidates must have a distance ∆R > 0.4 from any jet with pT > 20 GeV. Muons arising from cosmic
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