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

Chapter 2: The Accelerator and the Experiment 54
traverses at least three chambers, referred to as a projective tower (Figure 2.11). The
total number of channels in the drift chambers is 339,000.
Figure 2.9: The structure of a barrel MDT chamber. Two multilayers of drift tubes
and the spacer bars can be seen. The paths of the alignment rays are shown in red.
Cathode Strip Chambers (CSCs): In the very forward region, MDTs suffer
from high occupancy because of the large particle flux 5 . In the pseudorapidity range
2.0 < |η| < 2.7, CSCs are used instead of MDTs on the endcap wheel closest to
the interaction point. The CSCs are multiwire proportional chambers. The mode of
operation is similar to that of drift tubes in that charged particles create avalanches
of electron-ion pairs in the gas. Each chamber contains four alternating planes of
anode wires and cathode strips. The signal from a given track is collected on several
5 The safe limit of operation for an MDT is a flux of ≈ 150 Hz/cm 2 .