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

measure predominantly the energy of hadrons. In each of them the calorimeter consists of a metal matrix
with regularly spaced longitudinal channels filled with the electrode structure (concentric rods and tubes) pa-
rallel to beam axis. The sensitive medium is LAr and fills the gap between the rods and tubes and the matrix.
3.3.4 Muon Detectors
The muon spectrometer is the outer most ATLAS sub-detector. It is designed to detect charged particles
exiting the barrel and end-cap calorimeters. Due to the deflection of muon tracks in the presence of the
toroidal magnetic field, muon tracks are identified and reconstructed, and their momenta is measured in the
|η| < 2.7 range. Information from both the muon spectrometer and the inner detector can be matched to give
combined muon tracks. The spectrometer is also designed to trigger on those particles in the region η < 2.4.
The performance goal is a stand-alone pT resolution of ∼ 10% for 1 TeV tracks. Muon momenta down to
a few GeV (∼ 3 GeV, due to energy loss in the calorimeters) can be measured by the spectrometer alone [64].
In the barrel region, muon chambers are arranged in three cylindrical layers (‘stations’) around the beam
axis; in the transition and end-cap regions, the chambers are installed vertically, also in three stations.
Over most of the η range, Monitored Drift Tubes (MDTs) provide a precision measurement of the track
coordinates in the principal bending direction of the magnetic field. At large η, and close to the interaction
point, Cathode Strip Chambers (CSCs), with finer granularity, are used to cope with the demanding rate
and background conditions, due to their higher rate capability and time resolution. The MDTs chambers
consist of three to eight layers of drift tubes, operated at an absolute pressure of 3 bar. The mechanical
isolation in the drift tubes of each sense wire from its neighbors guarantees a robust operation. The CSCs
are multiwire proportional chambers with cathodes segmented into strips in orthogonal directions. This
allows both coordinates to be measured from the induced-charge distribution. The resolution of a chamber
is 40 µm in the R − z plane and ∼ 5 mm in the R − φ plane [64,65,69].
The precision-tracking chambers are complemented by a system of fast trigger chambers, covering a range
of |η| < 2.4. Resistive Plate Chambers (RPCs) are used in the barrel, |η| < 1.05, and Thin Gap Chambers
(TGCs) in the end-cap region, 1.05 < |η| < 2.4. Both types of trigger chambers also provide a ‘second
coordinate’ measurement of track coordinates orthogonal to the precision measurement, in approximately
the phi direction. The trigger chambers provide not only well-defined pT threshold, but also bunch-crossing
(BC) identification. The RPC is a gaseous parallel electrode-plate detector providing a typical space-time
33