Abstract
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.
Highlights
Precision mapping of the material within the tracking volume of the CMS detector [1] is important for the experiment’s measurement goals
For the design of the Phase-1 upgrade of the pixel detector, which was installed in Spring 2017, nuclear interactions (NIs) imaging was used to conclude that the sagging of the beam pipe between the supports was small enough to be of no concern
The values of the parameters are tabulated for the fits to the beam pipe with a circle, the barrel pixel (BPIX) detector inner shield with two half-circles, and the pixel detector support tube with an ellipse
Summary
Precision mapping of the material within the tracking volume of the CMS detector [1] is important for the experiment’s measurement goals. The analysis presented here uses reconstructed NIs to precisely measure the positions of inactive elements surrounding the proton-proton collision point, such as the beam pipe and the inner mechanical structures of the pixel detector. This information is needed to validate simulations of the CMS detector and to identify any shifts in the positions of inactive elements. For the design of the Phase-1 upgrade of the pixel detector, which was installed in Spring 2017, NI imaging was used to conclude that the sagging of the beam pipe between the supports was small enough to be of no concern Both the original and new versions of the CMS pixel detector are split into two half-cylinders and inserted by sliding these two halves into place by means of appropriate rails.
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