CMS silicon tracker alignment strategy with the Millepede II algorithm

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Abstract
The positions of the silicon modules of the CMS tracker will be known to O(100 μm) from survey measurements, mounting precision and the hardware alignment system. However, in order to fully exploit the capabilities of the tracker, thes e positions need to be known to a precision of a few μm. Only a track-based alignment procedure can reach this required precision. Such an alignment procedure is a major challenge given that about 50000 geometry constants need to be measured. Making use of the novel χ 2 minimization program Millepede II an alignment strategy has been developed in which all detector components are aligned simultaneously and all correla- tions between their position parameters taken into account. Different simulated data, such as Z0 decays and muons originated in air showers were used for the study. Additionally information about the mechanical structure of the tracker, and initial p osition uncertainties have been used as input for the alignment procedure. A proof of concept of this alignment strategy is demonstrated using simulated data.

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