The HIP Algorithm for Track Based Alignment and its Application to the CMS Pixel Detector

Good geometrical alignment is essential to fully benefit from the excellent intrinsic resolution of the CMS silicon tracker. Since the tracker consists of about 20000 independent silicon sensors, of the order 100k parameters are needed for the alignment. The determination of these constants with the required precision of about 10 um is an extremely challenging task. In this paper an effective and computationally practical alignment algorithm is presented. it is suitable for performing fine-calibration of the position and orientation of detector structures consisting of a number of pixel or strip modules as well as the alignment of individual modules. The performance of the algorithm is studied by applying it to the alignment of the CMS Pixel detector.