The FEE Server Control Engine of the ALICE-TRD - Westfälische ...

4 The ALICE Transition Radiation Detector
The ALICE Transition Radiation Detector (TRD) is located just outside the TPC in radial
direction, starting at a radius of 2.9 m and extending to 3.7 m. It is designed to fulfill
three tasks. The first one is electron-pion separation at momenta in excess of 1 GeV/c. In
this energy region the pion identification via energy loss measurement in the TPC is no
longer sufficient. Second, the TRD is a fast tracker. Therefore it can be used as a trigger
for high transverse momentum electrons or jets with high Et. Especially when looking
for rare particles such a trigger is necessary to enhance the statistical significance of the
measurement. Third the TRD adds up to six more points to the ITS/TPC tracks. Since the
TRD is located outside the TPC in radial direction the integrated effect of the magnetic
field to the particle trajectory is higher then inside the TPC. So the trajectory points from
the TRD increase the momentum resolution of ALICE significantly.
4.1 Detector Design and Mode of Operation
Figure 4.1: One half of the TRD with the TPC inside shown, too. Each supermodule has five stacks
(green, red, yellow, red, green) with 6 layers per stack.
The TRD is build out of 18 supermodules in azimuthal direction. Each supermodule
is about 7 m long and covers a pseudo-rapidity of |η| = 0.9. It is built out of 30 Readout
23