Precision measurement of the structure of the CMS inner tracking system using nuclear interactions

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.

Search for long-lived particles decaying to leptons with large impact parameter in proton–proton collisions at $$\sqrt{s} = 13\,\text {Te}\text {V} $$

“…To remove pairs of leptons from material interactions, we reject events where the candidate leptons form a good displaced vertex that overlaps with the tracker material, which is measured in Ref. [ 60 ]. The vertices are reconstructed with the Kalman vertex fitter [ 61 , 62 ], and a “good” vertex is one with a position uncertainty of less than 10 and a , where is the number of degrees of freedom of the fit.…”

Speeding up Particle Track Reconstruction using a Parallel Kalman Filter Algorithm

“…For the CMS Phase I geometry, we include the effects of multiple scattering and energy loss by defining two-dimensional arrays, indexed in r-z, with values of the radiation length and the material composition term in the Bethe-Block formula [21][22][23]. These constants account for the amount of material a particle would have to traverse in propagating from module to module.…”

High Quality QCD Axion and the LHC

“…Other SM background from metastable SM hadron decays can be effectively vetoed with the number of displaced tracks and vertexing requirements; for more detailed considerations, see the Supplemental Material [73] including Refs. [101][102][103][104].…”