The transition radiation tracker of the ATLAS experiment

The transition radiation tracker (TRT) is one of the three subsystems of the inner detector of the ATLAS experiment. It combines electron identification capability with charged-particle track reconstruction. A total of 420 000 electronic channels provide continuous tracking with many projective measurements per track. This paper gives details of some features of the TRT, from performance requirements to the consequences of its operation in the LHC environment. Some technical choices and operating conditions have been recently changed, the most significant one being the active gas. Presently, a large fraction of barrel and end-cap modules have been assembled in the United States and Russia, respectively. A strict quality assessment has been implemented at the assembly sites and at CERN upon arrival of the modules. The acceptance tests include dimensional surveys, wire-tension measurements, gas-tightness tests, high-voltage training, and gas-gain uniformity measurements along each individual straw. First estimates of the module quality are presented based on the analysis of these tests.