all these detectors allow precision measurement of charged particles trajectories in the environment of numerous tracks, but the Pixel contributes mainly to accurately measure vertices, the SCT to precisely measure the particle momenta
and the TRT to ease the pattern recognition with its very large number of close hits (while also contributing to electron identification). The figure illustrates the layout and shows that each detector consists of barrel and endcap regions in order to minimize the material traversed by particles coming from the interaction vertex.