  The structure of the CMS inner tracking system has been studied using nuclear
interactions of hadrons striking its material. Data from proton-proton
collisions at a center-of-mass energy of 13 TeV recorded in 2015 at the LHC are
used to reconstruct millions of secondary vertices from these nuclear
interactions. Precise positions of the beam pipe and the inner tracking system
elements, such as the pixel detector support tube, and barrel pixel detector
inner shield and support rails, are determined using these vertices. These
measurements are important for detector simulations, detector upgrades, and to
identify any changes in the positions of inactive elements.
