Measurement of the Z boson cross-section in - Harvard University ...

Chapter 2: The Accelerator and the Experiment 60
smaller than the distance between adjacent anode wires. This feature and the high
applied potential of 3100 V ensure fast signal generation. The anode wires are ar-
ranges parallel to the MDT wires, while the cathode (readout) strips run in the radial
direction. This configuration enables measurement of both the radial and azimuthal
coordinates. The spatial resolution of a TGC chamber is 2-6 mm in r and 3-7 mm in
φ. The time resolution is 4 ns. The signal arrives within a 25 ns time window with a
probability of 99%. The total number of TGC channels is 318,000.
As in the case of the RPCs, triggering in the TGCs uses a coincidence condition
in two or more trigger stations, depending on the track pT . Coincidence is required in
both the η and φ projections, thus minimizing the probability of accidental triggers
caused by random combinations of converted photons.
Magnetic field in the muon system
The toroids that provide the magnetic field for the muon spectrometer have been
briefly described in Section 2.2.1. The barrel toroid covers the pseudorapidity range
|η| < 1.4, and has a bending power of 1.5-5.5 Tm. The endcap toroids cover the
region 1.6 < |η| < 2.7, providing a bending power of 1-7.5 Tm. In the transition
region 1.4 < |η| < 1.6, the field is provided by both the barrel and endcap toroids,
which leads to considerable field inhomogeneity. The bending power is smaller in the
transition region than in the barrel and endcaps.
In order to satisfy the precision required of the muon system, the magnetic field
in the spectrometer must be accurately reconstructed. To this end, all three com-
ponents of the field are continuously monitored by ≈ 1800 Hall sensors throughout