CMS silicon tracker alignment strategy with the Millepede II algorithm

The positions of the silicon modules of the CMS tracker will be known to O(100 mum) from survey measurements, mounting precision and the hardware alignment system. However, in order to fully exploit the capabilities of the tracker, these positions need to be known to a precision of a few mum. 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 nove l I (2) minimization program Millepede II an alignment strategy has been developed in which all detector components are aligned simultaneously and all correlations between their position parameters taken into account. Different simulated data, such as Z(0 ) decays and muons originated in air showers were used for the study. Additionally information about the mechanical structure of the tracker, and initial position uncertainties have been used as input for the alignment procedure. A proof of concept of thi s alignment strategy is demonstrated using simulated data.