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One of the building blocks of the CMS Silicon Tracker: a part of the detector that reconstructs the trajectories of charged particles emerging from the proton-proton collisions. A lightweight structure, made mostly of carbon fibre, supports silicon detectors and their readout electronics. These detectors generate an electrical pulse when they are traversed by a charged particle, and they are segmented into fine strips (in this case the strips are 180 microns wide, about the size of a human hair) that collect those pulses, such that the position of the strip provides a coordinate on the particle trajectory. In this “rod” silicon detectors are arranged in back-to-back pairs, where the two detectors of each pair have the strips oriented at an angle, such that the crossing point of the strips provides a two-dimensional coordinate in the rod plane. Three pairs of detectors are mounted on each side of the rod structure, to fully cover its surface. In the Tracker, rods are arranged to form cylindrical layers in the central “barrel” region.