Measurement of the structure of the inner tracking detector of the CMS experiment using nuclear interactions with data collected in 2015

The material in the tracker system has been studied using nuclear interactions caused by particles traversing the detector material. The data was recorded in proton-proton collisions at 13 TeV by the CMS experiment at the LHC. The nuclear interactions are reconstructed as secondary vertices. We observe the structure of the inner part of the tracker, in particular, the inactive elements such as the beam pipe, the pixel shield, the pixel support, and the pixel support rails, and measure their positions. These measurements are particularly important for the pixel phase 1 upgrade.