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

large air-core toroids (one barrel and two end-caps) generating the magnetic field for the muon spectrome-
ter. The peak magnetic field on the superconductors in the barrel and end-cap toroids are 3.9 and 4.1 T
respectively. The two end-cap toroids (ECT) are inserted in the barrel toroid (BT) at each end and line up
with the CS. Each of the three toroids consists of eight coils assembled radially and symmetrically around
the beam axis. The ECT coil system is rotated by 22.5 ◦ with respect to the BT system in order to provide
radial overlap and to optimize the bending power in the interface regions of both coil systems. The bending
power between the inner and outer radius of the toroids is between 1.5 and 5.5 Tm for the BT, and between
1 to 7.5 Tm in the region 1.6 < |η| < 2.7 for the ECT. The bending power is lower in the transition regions
where the two magnets overlap (1.4 < |η| < 1.6) [64–66].
3.3.2 Tracking
The inner detector tracking system is mainly designed to reconstruct tracks and vertices with high efficiency,
perform precise measurements of leptons, and have good identification of individual particles in dense jets.
Charged particles trajectories are reconstructed and their momenta measured due to the 2 T magnetic field
generated by the central solenoid. Figure 3.3(b) shows the Inner Detector layout. It combines high-resolution
detectors at inner radii with continuos tracking elements at outer radii. The former is achieved with semi-
conductor detectors, whereas the latter one is provided by the TRT.
The pixel and SCT precision tracking detectors cover the region of |η| < 2.5, with about 80.4 and 6.3
million readout channels respectively. The Pixel detector is a high-granularity tracking detector designed
to provide a set of measurements as close to the interaction point as possible. The system consists of three
concentric barrels at average radii of ∼ 4 cm, 11 cm, and 14 cm from the beam axis, and four disks on
Detector Component Required resolution
Tracking σpT /pT = 0.05% pT ⊕ 1% ±2.5
η coverage
Measurement Trigger
EM calorimetry σE/E = 10%/ √ E ⊕ 0.7% ±3.2 ±2.5
Hadronic calorimetry (jets)
barrel and end-cap σE/E = 50%/ √ E ⊕ 3% ±3.2 ±3.2
forward σE/E = 100%/ √ E ⊕ 10% 3.1 < |η| < 4.9 3.1 < |η| < 4.9
Muon spectrometer σpT /pT = 10% at pT = 1 TeV ±2.7 ±2.4
Table 3.2: General performance goals of the ATLAS detector. The units for E and pT are in GeV. For
high-pT muons the muon spectrometer performance is independent of the inner-detector system.
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