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

The positive x-direction is defined as pointing from the interaction point to the center of the LHC ring
and the positive y-axis is defined as pointing upwards. The azimuthal angle, φ, is measured around the
beam axis, and the polar angle θ is the angle from the beam axis. The pseudorapidity is defined as
η ≡ −ln tan(θ/2). The distance between objects 1 and 2 in the pseudorapidity-azimuthal angle space,
is defined as ∆R ≡ (φ1 − φ2) 2 + (η1 − η2) 2 . The transverse momentum, pT, is defined as psin θ, where p
is the momentum. The transverse energy, ET, is defined as E sin θ, where E is the energy measured in the
calorimeter, and θ is the polar angle of the energy deposition.
Figure 3.2 shows a cut-away view of the detector, where the layout of the different components can be
appreciated. Figure 3.3 displays these components separately. Table 3.2 provides a summary of expected
energy-momentum resolution of each component, along with their coverage in η.
3.3.1 Magnet System
Figure 3.2: Cut-away view from the ATLAS detector [64].
The ATLAS superconducting magnet system can be seen in Figure 3.3(a). It consists of a thin central
solenoid (CS), providing the inner detector with a 2 T axial magnetic field, surrounded by a system of three
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